NORTH AMERICAN VACCINE INC
SC 13D/A, 1999-07-28
BIOLOGICAL PRODUCTS, (NO DIAGNOSTIC SUBSTANCES)
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<PAGE>   1
                                                               Page 1 of 7 Pages


                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549


                                  SCHEDULE 13D


                    UNDER THE SECURITIES EXCHANGE ACT OF 1934
                               (AMENDMENT NO. 8)*


                          North American Vaccine, Inc.
- --------------------------------------------------------------------------------
                                (Name of Issuer)


                           Common Stock, No Par Value
- --------------------------------------------------------------------------------
                         (Title of Class of Securities)


                                   657-201-109
- --------------------------------------------------------------------------------
                                 (CUSIP Number)

   Charles-A. Tessier, Vice-President, Legal Affairs and General Counsel
              BioChem Pharma Inc., 275 Armand Frappier Boulevard,
                          Laval, Quebec H7V 4A7 Canada
- --------------------------------------------------------------------------------
           (Name, Address and Telephone Number of Person Authorized to
                       Receive Notices and Communications)


                                July 21, 1999
- --------------------------------------------------------------------------------
             (Date of Event which Requires Filing of this Statement)

If the filing person has previously filed a statement on Schedule 13G to report
the acquisition which is the subject of this Schedule 13D, and is filing this
schedule because of Rule 13d-1(b)(3) or (4), check the following box / /.

*The remainder of this cover page shall be filled out for a reporting person's
initial filing on this form with respect to the subject class of securities, and
for any subsequent amendment containing information which would alter
disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed
to be "filed" for the purpose of Section 18 of the Securities Exchange Act of
1934 ("Act") or otherwise subject to the liabilities of that section of the Act
but shall be subject to all other provisions of the Act (however, see the
Notes).
<PAGE>   2

                                  SCHEDULE 13D

CUSIP NO. 657-201-109                                         Page 2 of 7 pages
- -------------------------------------------------------------------------------
1   NAME OF REPORTING PERSON
    S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON

    BIOCHEM PHARMA INC.
- -------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*
                                                                         (a) / /
                                                                         (b) / /
- -------------------------------------------------------------------------------
3   SEC USE ONLY


- -------------------------------------------------------------------------------
4   SOURCE OF FUNDS*

    WC
- -------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
    TO ITEMS 2(D) OR 2(E)                                                   / /
- -------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION


Laval, Quebec, Canada
- -------------------------------------------------------------------------------
                7   SOLE VOTING POWER
  NUMBER OF
   SHARES           15,040,704
BENEFICIALLY   ----------------------------------------------------------------
  OWNED BY      8   SHARED VOTING POWER
   EACH
 REPORTING
  PERSON       ----------------------------------------------------------------
   WITH         9   SOLE DISPOSITIVE POWER

                    15,040,704
               ----------------------------------------------------------------
               10   SHARED DISPOSITIVE POWER


- -------------------------------------------------------------------------------
11   AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

     15,040,704
- -------------------------------------------------------------------------------
12   CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES
     CERTAIN SHARES*                                                        / /
     n/a
- -------------------------------------------------------------------------------
13   PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

     41.6%
- -------------------------------------------------------------------------------
14   TYPE OF REPORTING PERSON*

     CO
- -------------------------------------------------------------------------------
                     *SEE INSTRUCTIONS BEFORE FILLING OUT!
<PAGE>   3

                                                              Page 3 of 7 Pages
Item 1.  Security and Issuer.

         This Amendment relates to the common stock, no par value (the "Common
Stock") of North American Vaccine, Inc. (the "Company"), 12103 Indian Creek
Court, Beltsville, Maryland, U.S.A. 20705.


Item 2.  Identity and Background.

         This Amendment is being filed by BioChem Pharma Inc. ("BioChem").
BioChem is a publicly-owned Canadian pharmaceutical company incorporated under
the laws of Canada. BioChem has specialized since 1986 in the research,
development, manufacture and sale of products for the diagnosis, treatment and
prevention of human diseases. The principal executive offices of BioChem are at
275 Armand-Frappier Boulevard, Laval, Quebec, H7V 4A7 and its telephone number
is (450) 681-1744.

         A list of BioChem's Directors and Executive Officers is included as
Exhibit 5 to this Amendment.

         Neither BioChem, nor, to the best of BioChem's knowledge, any of
BioChem's Directors or Executive officers has during the last five years, or
at any time prior thereto: (a) been convicted in any criminal proceeding
(excluding traffic violations or similar misdemeanors); or (b) been party to
a civil proceeding of a judicial or administrative body of competent
jurisdiction resulting in its having been or being subject to a judgement,
decree or final order enjoining future violations of, or prohibiting or
mandating activities subject to, federal or state securities laws or
finding any violation with respect to such laws.

Item 3.  Source and Amount of Funds or Other Consideration.

     On July 1, 1999, BioChem executed an Agreement (the "Agreement"), whereby
BioChem agreed to provide an unsecured guaranty (the "Guaranty") for a line of
credit (the "Line of Credit") that the Company was seeking to secure from Royal
Bank of Canada. In consideration of BioChem's agreement to provide the Guaranty,
the Company has agreed to grant BioChem warrants (each a "Warrant" and
collectively, the "Warrants") to purchase up to 750,000 shares of the Company's
Common Stock (the "Warrant Shares") at an exercise price of $5.14 per share,
subject to adjustment. The Company will issue the Warrants to BioChem as
follows: for each U.S. $1 million (or fraction thereof) of principal amount
drawn by the Company under the Line of Credit, the Company shall issue to
BioChem a Warrant to purchase 125,000 shares of the Company's Common Stock. Each
Warrant will be exercisable immediately upon issuance by the Company.

     As of the date hereof, the Company has issued 250,000 Warrants to BioChem.
BioChem expects to use its working capital to fund the purchase of any Warrant
Shares upon grant and exercise of any Warrants.



<PAGE>   4

                                                              Page 4 of 7 Pages

Item 4.  Purpose of Transaction

         BioChem intends to maintain its interests in the securities of the
Company (including the Notes (as defined below)) as an investment. BioChem may
acquire additional shares of Common Stock or other securities of the Company
(subject to availability of such securities at prices deemed favorable) in the
open market, in privately negotiated transactions, by tender offer or
otherwise. Alternatively, BioChem reserves the right to dispose of some or all
of its shares of the Company's Common Stock (including any obtained upon
conversion of the Notes or exercise of the Options (as defined below) or
Warrants) in the open market or in privately negotiated transactions or
otherwise depending upon the courses of action that BioChem or the Company
pursues, market conditions and other factors. Although the foregoing represents
the range of activities presently contemplated by BioChem with respect to the
shares of the Company's Common Stock, it should be noted that possible
activities of BioChem are subject to change at any time.

         Except as otherwise stated herein, BioChem has no present plans or
proposals which relate to or would result in any actions described in
subparagraphs (a) through (j) of Schedule 13D.

Item 5.  Interest in Securities of the Issuer.

         (a) BioChem owns 11,179,114 shares of the Company's Common Stock,
1,000,000 shares of the Company's Class A Preferred Stock, options to purchase
57,812 shares of the Company's Common Stock (the "Options"), $9,000,000
principal amount of the Company's 4.5% convertible secured notes due 2003 (the
"Notes") which are convertible into the Company's Common Stock. Assuming grant
and exercise of all the Warrants BioChem would beneficially own an aggregate
amount of 15,040,704 of the Company's Common Stock representing 41.6% of the
Company's Common Stock.

         (b) The amount disclosed includes 1,000,000 shares of the Company's
Class A Preferred Stock which are convertible into 2,000,000 shares of the
Company's Common Stock, 57,812 shares of the Company's Common Stock which may
be purchased upon the exercise of stock options currently exercisable,
1,053,778 shares of the Company's Common Stock into which the Notes are
currently convertible and 750,000 of the Warrant Shares. BioChem disclaims
beneficial ownership of 500,000 of the Warrant Shares until the relevant
Warrants are granted and become exercisable.
<PAGE>   5
                                                              Page 5 of 7 Pages

         (c) BioChem has sole and exclusive voting and dispositive power with
respect to all shares of the Company's Common Stock and Class A Preferred Stock.

Item 6.  Contracts, Arrangements, Understandings or
         Relationships With respect to Securities of the Issuer.

         No change from the Schedule 13D as originally filed and subsequently
amended except as set forth below.

         The Company has agreed to include the Warrant Shares in the definition
of "Registrable Securities" as that term is defined in Schedule 4 to the Share
Purchase Agreement by and between the Company and BioChem dated January 17,
1990, as amended (the "Share Purchase Agreement"). Therefore, the Warrant Shares
shall be subject to all terms and conditions of BioChem's registration rights as
specified in Section One of Schedule 4 to the Share Purchase Agreement.

         The description of the agreements contained herein is not intended to
be complete and is qualified in its entirety by reference to such agreements
which are attached hereto as Exhibits 1 through 4 and incorporated herein by
reference.


Item 7.  Material to be Filed as Exhibits.

         1.       Agreement, dated July 1, 1999, by and between the Company and
                  BioChem, regarding the provision of the Guaranty and the
                  granting of the Warrants.

         2.       Form of Guaranty, in favor of Royal Bank of
                  Canada regarding the Line of Credit.

         3.       Form of Warrant (Contained in Exhibit 1).

         4.a      Share Purchase Agreement dated January 17, 1990 by and
                  between the Company and BioChem.

         4.b      Amendment to Share Purchase Agreement dated as of January 8,
                  1998 between the Company and BioChem.

         5.       List of BioChem's Directors and Executive Officers

<PAGE>   6
                                                               Page 6 of 7 Pages

                                    Signature


         After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.


                                                  BIOCHEM PHARMA INC.

                                              By: /s/ Charles-A. Tessier
                                                  -----------------------------
                                                  Charles-A. Tessier
                                                  Vice-President, Legal Affairs
                                                  and General Counsel


Dated: July 27, 1999
<PAGE>   7
                                                               Page 7 of 7 Pages


                                  EXHIBIT INDEX


         1.       Agreement, dated July 1, 1999, by and between the Company and
                  BioChem, regarding the provision of the Guaranty and the
                  granting of the Warrants.

         2.       Form of Guaranty, in favor of Royal Bank of
                  Canada regarding the Line of Credit.

         3.       Form of Warrant (Contained in Exhibit 1).

         4.a      Share Purchase Agreement dated January 17, 1990 by and
                  between the Company and BioChem.

         4.b      Amendment to Share Purchase Agreement dated as of January 8,
                  1998 between the Company and BioChem.

         5.       List of BioChem's Directors and Executive Officers.


<PAGE>   1
                                                                    July 1, 1999
BioChem Pharma Inc.
275 Armand Frappier Blvd
Laval, Quebec H7V 4A7
Canada

Re:      Guaranty of $6 Million (US) Line of Credit

Gentlemen:

         As you know, North American Vaccine, Inc. ["NVX"] is presently seeking
a line of credit [the "Line of Credit"] from Royal Bank of Canada in the
principal amount of Six Million Dollars (US) [$6,000,000 (US)] [the "Principal
Amount"]. The bank has indicated its intention to provide the Line of Credit in
the Principal Amount to NVX in accordance with the term sheet a copy of which
attached hereto provided that it receives an unsecured guaranty [the "Guaranty"]
from BioChem Pharma Inc. ["BioChem"] in favor of, and in a form acceptable to,
the bank supporting all amounts drawn down under the Line of Credit.

         This letter is to confirm the agreement between NVX and BioChem under
which BioChem will provide the Guaranty of up to the Principal Amount to support
the Line of Credit proposed to be extended to NVX by Royal Bank of Canada, or
any other mutually acceptable lending institution ["Lender"].

1.       PROVISION OF GUARANTY
1
       2 a. Subject to approval by its board of directors, which shall be
obtained on or before July 9, 1999, BioChem hereby agrees to provide the
Guaranty in favor of, and in a form acceptable to, the Lender up to the
Principal Amount. The Guaranty shall be furnished to the Lender in consideration
of the Lender's commitment to extend a Line of Credit to NVX in the Principal
Amount. BioChem shall execute and deliver such documents and agreements as may
be required by the Lender to implement the Guaranty in favor of the Lender
within five (5) business days of receiving the request of the Lender. BioChem
shall not be required to provide the Guaranty if the Lender does not provide the
Line of Credit to NVX.

         b. BioChem agrees that the Guaranty shall remain in effect for a period
of not less than twenty-four (24) continuous months ["Guaranty Period"] to
support the Line of Credit and/or any successor line of credit or other credit
facility obtained by or for NVX; provided, however, at no time shall the
Guaranty exceed the Principal Amount and provided further that no successor line
of credit or other credit facility contain terms and condition that are less
favorable to NVX than those contained in the Line of Credit collateralized by
the Guaranty and provided further that no successor line of credit or other
credit facility that will be collateralized by the Guaranty shall be entered
into by NVX without BioChem's express written consent that will not be
unreasonably withheld, conditioned or delayed.
<PAGE>   2
BioChem Pharma Inc.
July 1, 1999
Page 2 of 8

         c. BioChem agrees to provide NVX with all reasonable cooperation and
assistance in obtaining a successor or replacement line of credit, loan or
credit facility for NVX if the Line of Credit expires unrenewed or unextended
before the expiration of the Guaranty Period, including without limitation
executive and delivery of all documents requested by Lender; provided, however
that such cooperation shall not be more onerous to BioChem than that required of
it in the initial issuance of the Guaranty and provided further that the amount
of the successor or replacement line of credit that will be collateralized by
the Guaranty shall not exceed the Principal Amount.

         d. As a condition to BioChem's obligation to issue the Guaranty, NVX
agrees to give BioChem at least two (2) business days notice of its intention to
draw any borrowings under the Line of Credit. In addition, NVX understands, and
the relevant documents and agreements shall reflect to the greatest extent
possible, that BioChem's guarantee obligation under the Guaranty shall be one of
collection and that the Lender shall be required to exercise all commercially
reasonable remedies, short of litigation to final judgment, to satisfy NVX's
obligations under the Line of Credit prior to requiring payments by BioChem
pursuant to the Guaranty.

2. ISSUANCE OF WARRANT In consideration of BioChem providing the Guaranty to the
Lender as contemplated by Article 1 above, NVX agrees that it shall issue to
BioChem one or more Stock Purchase Warrant(s) (individually referred to herein
as the "Warrant" and collectively referred to herein as the "Warrants") in form
and content substantially the same as that attached hereto and incorporated
herein by this reference on the following terms and conditions:

         a. The exercise price of the Warrants shall be the average of the
closing prices of the common stock of NVX on the American Stock Exchange over a
period of five trading days commencing on June 28, 1999 and ending July 2, 1999.

         b. If the Line of Credit is drawn down by NVX for the full amount of
the Principal Amount, BioChem shall be entitled to one or more Warrant(s) to
purchase a total of Seven Hundred Fifty Thousand (750,000) shares of common
stock of NVX. Accordingly, a Warrant shall be issued ratably as NVX draws down
on the Line of Credit as follows: for each One Million Dollars (US) [$1,000,000
(US)] (or fraction thereof) of principal amount drawn down by NVX under the Line
of Credit, NVX shall issue to BioChem a Warrant to acquire One Hundred Twenty
Five Thousand (125,000) shares of common stock of NVX.

         c. Each Warrant shall have a term of two (2) years from the date of
issuance and shall be non-negotiable and non-transferable except under the terms
and conditions set forth therein.

         d. The shares of common stock of NVX issuable upon exercise of each
Warrant [the "Warrant Shares"] shall be fully reserved for issuance at all times
during which the Warrant is issued and outstanding and, at the time of delivery
if such Warrant is duly and properly exercised, shall be validly issued and
outstanding, fully paid and non-assessable.
<PAGE>   3
BioChem Pharma Inc.
July 1, 1999
Page 3 of 8

3. TRANSFER RESTRICTIONS AND REPRESENTATIONS In connection with the issuance of
the Warrants and the Warrant Shares [collectively the "Securities"], BioChem
hereby acknowledges that the Securities will be issued to it pursuant to an
exemption from the registration provisions of the Securities Act of 1933, as
amended, and other applicable securities laws [collectively the "Securities
Acts"]. BioChem specifically acknowledges and agrees that:

         a. the purchase of the Securities involves a high degree of risk in
that an investment in the Company is highly speculative and BioChem may suffer a
loss of its entire investment;

         b. the transferability of the Securities will be limited as set forth
below and thus it may not be able to liquidate all or any portion of the
investment;

         c. it is able, either alone or with an investor representative, to
evaluate the merits and risks of this investment and that it recognizes the
highly speculative nature of this investment;

         d. it has had access to all information regarding NVX that it has
requested or desired to know, that all documents which could be reasonably
provided have been made available for its inspection and review and that it has
been afforded the opportunity to ask question of and receive answers from duly
authorized officers or other representatives of the NVX concerning this
transaction and any additional information that it has requested;

         e. the Securities are being acquired for its own account, for
investment purposes only and not with a view to distribution or resale to others
and that the exemption from the registration requirements of the Securities Act
being claimed by NVX for this transaction is dependent, in part, on BioChem's
investment intent;

         f. it understands there is no public market for the Warrants and none
is likely to develop;

         g. it is an "accredited investor" within the meaning of Section 2(15)
and/or Rule 501 under the Securities Act;

         h. it understands that the Securities are being offered in a
transaction not involving any public offering within the meaning of the
Securities Acts, that the Securities will not be registered under the Securities
Acts and that it may not resell, pledge or otherwise transfer any such
Securities except in accordance with the terms and restrictions contained in the
Warrants and in a transaction exempt from the registration requirements of the
Securities Acts.
<PAGE>   4
BioChem Pharma Inc.
July 1, 1999
Page 4 of 8

         i. it consents to the placement of a legend on the Securities stating
that they have not been registered under the Securities Acts and setting forth
or referring to the restrictions on transferability and sale thereof.

4. OTHER REPRESENTATIONS AND WARRANTIES

         a. BioChem represents and warrants as follows:

                  i BioChem is a corporation duly organized and existing under
the laws of Canada and has the corporate power to conduct the business that it
conducts and proposes to conduct;

                  ii Upon approval of this agreement by the Board of Directors
of BioChem, the execution, delivery and performance of this agreement by BioChem
will be duly approved by all necessary corporate action, and all other corporate
authorities, approvals and actions required to authorize BioChem to issue the
Guaranty and to receive the Warrants and purchase the Warrant Shares will have
been duly taken and approved;

                  iii The consummation of the transactions contemplated by this
agreement will not violate or constitute a default under BioChem's
organizational documents or any material agreements to which BioChem is a party
or by which its properties are bound or constitute a violation of any material
order, rule, regulation, writ, injunction, or decree of any government,
governmental instrumentality or court, domestic or foreign;

                  iv. It has not retained a placement or selling agent, broker
or dealer to represent it in the acquisition of the Warrants or the Warrant
Shares and no person has any claim or right to any commission or other
remuneration as a result of contract or agreement with BioChem in connection
with the execution or consummation of the transactions contemplated by this
agreement.

         b. NVX represents and warrants as follows:

                  i NVX is a corporation duly organized and existing under the
laws of Canada and has the corporate power to conduct the business that it
conducts and proposes to conduct;

                  ii The execution, delivery and performance of this agreement
by NVX has been duly approved by the Board of Directors of NVX and all other
corporate actions required to authorize and effect the issuance of the Warrants
and sale of the Warrant Shares have been duly taken and approved;

                  iii The Warrant Shares have been duly and validly authorized
and when issued and paid for in accordance with the terms and conditions of the
Warrants will be validly issued, fully paid and non-assessable shares of common
stock of NVX;
<PAGE>   5
BioChem Pharma Inc.
July 1, 1999
Page 5 of 8

                  iv. NVX is not in violation or default under, nor will the
execution and delivery of this agreement, the issuance of the Warrants or the
Warrant Shares and the incurrence of the obligations herein and therein set
forth and the consummation of the transaction contemplated hereby and thereby,
result in a violation of, or constitute a default under, NVX's certificate of
incorporation or by-laws;

                  v. The consummation of the transactions contemplated by this
agreement will not violate or constitute a default under any material agreements
to which NVX is a party or by which its properties are bound or constitute a
violation of any material order, rule, regulation, writ, injunction, or decree
of any government, governmental instrumentality or court, domestic or foreign.

                  vi. no consent, approval or filing with any governmental
authority or other party is required by NVX for the consummation of the
transactions contemplated by this agreement including in connection with the
issuance of the Warrants and the Warrant Shares other than the required and
applicable notices and filings to be made with the U.S. Securities & Exchange
Commission, notices, filings and approvals requited by state and provincial
securities regulatory authorities, and notices and listing agreements with the
American Stock Exchange.

5. REGISTRATION RIGHTS NVX and BioChem agree that the Warrant Shares shall be
included in the definition of "Registrable Securities" as that term is defined
in Schedule 4 to the Share Purchase Agreement between the parties dated January
17, 1990, as amended, ("Share Purchase Agreement") and that as such, the Warrant
Shares shall be subject to all terms and conditions of BioChem's registration
rights as specified in Section One of Schedule 4 to the Share Purchase
Agreement. As a consequence of this Section 5, the definition of "Registrable
Securities" as set forth in Schedule 4, Section 1.1 to the Share Purchase
Agreement is hereby modified to add new Subsections (iii) and (iv) at the end
thereof to read in its entirety as follows:

    "Registrable Securities" shall mean (i) the Common Shares, (ii) any NAVA
    common shares issued pursuant to the Options or issued or issuable in
    respect of the Common Shares, upon any stock split, stock dividend,
    recapitalization, or similar event, so long as the Common Shares and any
    NAVA common shares issued in respect of the Common Shares are owned by
    BioChem, (iii) any NAVA common shares issued pursuant to the exercise of one
    or more Warrant(s) ("Warrant Shares"), which Warrant or Warrants are granted
    to BioChem pursuant to the terms of that certain letter agreement dated July
    1, 1999 between NAVA and BioChem and (iv) any NAVA common shares issued or
    issuable in respect of the Warrant Shares, upon any stock split, stock
    dividend, recapitalization, or similar event, so long as the Warrant Shares
    and any NAVA common shares issued in respect of the Warrant Shares are owned
    by BioChem.

6. OTHER MATTERS

         a. No modification, amendment, deletion, addition or other change in
this
<PAGE>   6
BioChem Pharma Inc.
July 1, 1999
Page 6 of 8

agreement or any provision hereof, or waiver of any right or remedy herein
provided, shall be effective for any purpose unless specifically set forth in a
writing signed by the Party to be bound thereby. No waiver of any right in
respect of an occurrence or event on one occasion shall be deemed a waiver of
such right or remedy in respect of such occurrence or event on any other
occasion.

         b. Any notice required to be given hereunder shall be in English
language, in writing and shall be deemed to have been duly given and received
upon transmission when telecopied with verification of receipt or upon delivery
if sent by Federal Express, DHL or other internationally recognized overnight or
express courier. Addresses for the delivery of notices shall be as follows:

         For BioChem: BioChem Pharma Inc., 275 Armand Frappier Boulevard, Laval,
Quebec H7V 4A7, Canada; Attn: Chief Financial Officer ; Telecopy:
1-450-978-7755.

         For NVX: North American Vaccine, Inc.; 10150 Old Columbia Road;
Columbia, MD 21046 USA; Attn: Vice President Finance; Telecopy: (410) 309-4077

         c. Notwithstanding the place where this agreement may be executed by
any of the parties hereto, the parties expressly agree that all the terms and
provision hereof shall be construed in accordance with and governed by the laws
of the State of New York (regardless of the laws that might be applicable under
principles of conflicts of law), including without limitation as to all matters
of validity, construction, effect and performance.

         d. This agreement may be executed in one or more counterparts, each of
which shall be deemed to be an original but all of which together shall
constitute one and the same instrument.

         e. This agreement shall be binding on and inure to the benefit of the
parties hereto and to their respective successors and permitted assigns. This
agreement may not be assigned by operation of law, by "change of control" of NVX
or otherwise, without the express written consent of BioChem. For purposes of
this agreement, the term "change of control" shall include either of the
following events: (i) any "Person" and/or "Group" (as such terms are used in
Section 13(d) of the Securities Exchange Act of 1934, as amended, (the "Exchange
Act")] other than BioChem or its affiliates, becomes the beneficial owner (as
defined in Rules 13d-3 and 13d-5 under the Exchange Act] directly or indirectly
of more than thirty percent (30%) of NVX's total outstanding voting securities,
provided however the acquisition of beneficial ownership by such Person or Group
of more than thirty percent (30%) of NVX's total outstanding voting securities,
which acquisition was accomplished in whole or in part by virtue of a purchase
or a series of related purchases of securities, rights, or instruments from
BioChem and/or its affiliates, shall not be considered a change of control; or
(b) NVX consolidates or merges with or into any Person, or conveys, transfers,
leases or otherwise disposes of all or substantially all of its assets to any
Person, or any Person consolidates with or
<PAGE>   7
BioChem Pharma Inc.
July 1, 1999
Page 7 of 8

merges into NVX, in any such event pursuant to a transaction in which the
outstanding voting securities of NVX is converted into or exchanged for cash,
securities or other properties. In the event of a "change of control" of NVX,
BioChem shall have the right to cancel this agreement and the Guaranty. The
cancellation of this agreement and the Guaranty in connection with a change of
control of NVX shall in no way modify the terms and conditions of the Warrant(s)
that might have been issued by NVX to BioChem hereunder.

         f. This agreement sets forth the entire understanding of the parties as
to the subject matter hereof and merges and supercedes all prior discussions,
agreements and understandings of any and very nature among them.

         g. Each party agrees to take or cause to be taken such further actions,
to execute, deliver and file or cause to be executed, delivered and filed such
further documents and instruments, and to obtain such consents as may be
necessary or as may be reasonably requested in order fully to effectuate the
purposes, terms and conditions of this agreement.

         h. This agreement is written and executed in the English language. It
is understood that, for purposes of obtaining the regulatory approval of the
agreement by appropriate governmental authorities, that the text of this
agreement, if necessary, may be translated into appropriate language(s). In the
event of a difference in the meaning between the translated text and the English
text, the English text shall govern. Il est de la volonte expresse des
parties que cette convention et touts les documents s'y rattachant soient
rediges et signes en anglais.

                                     * * * *

         Please acknowledge your acceptance and agreement with the terms of this
agreement by signing and returning the enclosed copy of this letter.


                                                 Sincerely,

                                                 North American Vaccine, Inc.



                                                 By: /s/ Daniel J. Abdun-Nabi
                                                    ----------------------------
                                                 Name: Daniel J. Abdun-Nabi
                                                 Title:    Senior Vice President
                                                 Legal Affairs & General Counsel


ACCEPTED AND AGREED
this 1st day of July, 1999
<PAGE>   8
BioChem Pharma Inc.
July 1, 1999
Page 8 of 8



BioChem Pharma Inc



By: /s/ Francois Legault
    --------------------------------
Name:   Francois Legault
Title:  Executive Vice President DVT
        Corporate



By: /s/ Charles-A. Tessier
    --------------------------------
Name:   Charles-A. Tessier
Title:  Vice President Legal Affairs
        & General Counsel
<PAGE>   9
THIS WARRANT AND THE COMMON SHARES ISSUABLE UPON EXERCISE HEREOF HAVE NOT BEEN
REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED, OR UNDER THE SECURITIES
LAWS OF ANY STATE OF THE UNITED STATES OR PROVINCE OF CANADA AND SUCH SECURITIES
MAY NOT BE SOLD, PLEDGED OR OTHERWISE TRANSFERRED IN THE ABSENCE OF SUCH
REGISTRATION OR AN APPLICABLE EXEMPTION THEREFROM


                          NORTH AMERICAN VACCINE, INC.

                    Warrant for the Purchase of Common Shares

No.  W-1                                                    _____________ Shares


         FOR VALUE RECEIVED, NORTH AMERICAN VACCINE, INC. (the "Company"), a
Canadian corporation, hereby certifies that BioChem Pharma Inc. or its permitted
assigns (the "Holder") is entitled to purchase from the Company, at any time or
from time to time after the date set forth on the signature page, but prior to
5:00 p.m. on ___________, 200_, _________________ (_______) fully paid and
non-assessable common shares, no par value, of the Company for an aggregate
purchase price of $____________ (computed on the basis of $____ per share).
(Hereinafter, (i) said common shares, together with any other equity securities
which may be issued by the Company in substitution therefor, are referred to as
the "Common Shares", (ii) the Common Shares purchasable hereunder are referred
to as the "Warrant Shares", (iii) the aggregate purchase price payable hereunder
for the Warrant Shares is referred to as the "Aggregate Warrant Price", (iv) the
price payable hereunder for each of the Warrant Shares, as adjusted in the
manner set forth in Section 3, is referred to as the "Per Share Warrant Price"
and (v) this Warrant and all warrants hereafter issued in exchange or
substitution for this Warrant are referred to as the "Warrants") The Aggregate
Warrant Price is not subject to adjustment. The Per Share Warrant Price and the
number of Warrant Shares are subject to adjustment as hereinafter provided.

         1. Exercise of Warrant. This Warrant may be exercised, in whole at any
time or in part from time to time (such partial exercises to be in amounts of
not less than 1,000 Warrant Shares), on and after the date set forth on the
signature page, but prior to 5:00 p.m. on _____, 200_, by the Holder of this
Warrant by the surrender of this Warrant (with the subscription form at the end
hereof duly executed) at the principal office of the Company in Columbia, MD
together with proper payment of the Aggregate Warrant Price applicable on such
date, or the proportionate part thereof if this Warrant is exercised in part.
Payment for Warrant Shares shall be made by (i) check payable to the order of
the Company, (ii) wire transfer to an account designated by and in the name of
the Company, (iii) by delivery to the Company of debt securities for which it is
the issuer and bound to make payment in the stated principal amount, where the
principal amount on such debt security

                                       1
<PAGE>   10
delivered to the Company for retirement is equal to the Aggregate Warrant Price;
or (iv) by any combination of the methods set forth in (i) through (iii), above.
If this Warrant is exercised in part, this Warrant must be exercised for a
number of whole Warrant Shares, and the Holder is entitled to receive a new
Warrant covering the number of Warrant Shares in respect of which this Warrant
has not been exercised and setting forth the proportionate part of the Aggregate
Warrant Price applicable to such Warrant Shares. Upon such surrender of this
Warrant, the Company will issue a certificate or certificates in the name of the
Holder for the largest number of whole Warrant Shares to which the Holder shall
be entitled and, if this Warrant is exercised in whole, in lieu of any
fractional Warrant Share to which the Holder shall be entitled, cash equal to
the fair value of such fractional share (determined in such reasonable manner as
the Board of Directors of the Company shall determine).

         2. Reservation of Warrant Shares. The Company agrees that, prior to the
expiration of this Warrant, the Company will at all times have authorized and
reserve, and will keep available, solely for issuance or delivery upon the
exercise of this Warrant, the Warrant Shares free and clear of all restrictions
on sale or transfer (except as may arise under applicable securities laws) and
free and clear of all preemptive rights.

         3. Protection Against Dilution. (a) If, at any time or from time to
time after the date of this Warrant, the Company shall (i) issue to the holders
of the Common Shares any Common Shares by way of a stock dividend; (ii)
subdivide its outstanding Common Shares into a greater number of shares; (iii)
combine its outstanding number of Common Shares into a smaller number (i.e., a
reverse stock split); or (iv) issue by reclassification of its Common Shares any
shares of capital stock of the Company then, and in each such case, the Per
Share Warrant Price in effect immediately prior to the date of such action shall
be adjusted, or further adjusted, to a price (to the nearest cent) determined by
dividing (x) an amount equal to the number of Common Shares outstanding
immediately prior to such issuance multiplied by the Per Share Warrant Price in
effect immediately prior to such issuance by (y) the total number of Common
Shares outstanding immediately after such issuance. Upon each adjustment in the
Per Share Warrant Price resulting from a stock split or stock dividend, the
number of Warrant Shares shall be adjusted by dividing the Aggregate Warrant
Price by the Per Share Warrant Price in effect immediately after such
adjustment. Notice of each such adjustment and each such readjustment shall be
forthwith mailed to the Holder.

         (b) If the Company shall be consolidated with or merged into another
corporation, or shall sell all or substantially all of its assets as part of a
reorganization to which the Company is a party within the meaning of the
Internal Revenue Code of 1986, as presently in effect, or shall issue a security
convertible into its Common Shares as a dividend on its Common Shares, each
Warrant Share shall be replaced for the purposes hereof by the securities or
properties issuable or distributed in respect of one Common Share upon such
consolidation, merger, sale, reclassification or reorganization, and adequate
provisions to that effect shall be made at the time thereof. Notice of

                                       2
<PAGE>   11
such consolidation, merger, sale, reclassification or reorganization, and of
said provisions so proposed to be made, shall be mailed to the Holder not less
than 15 days prior to such event.

         (c) If the Board of Directors of the Company shall declare any dividend
or other distribution in cash with respect to the Common Shares, other than out
of surplus, the Company shall mail notice thereof to the Holder not less than 15
days prior to the record date fixed for determining shareholders entitled to
participate in such dividend or other distribution.

         (d) If , during the term of this Warrant, the Company shall issue or
sell its Common Shares for a consideration per share less than the Per Share
Warrant Price immediately prior to the time of such issue or sale, then
forthwith upon such issue or sale, the Per Share Warrant Price in effect
immediately prior to such issue or sale shall be reduced to the lower of the
prices (calculated to the nearest cent) determined as follows:

                  (1) by dividing (A) an amount equal to the sum of (i) the
         number of shares of Common Stock outstanding immediately prior to such
         issue or sale multiplied by the then-existing Per Share Warrant Price,
         and (ii) the consideration, if any, received by the Company upon such
         issue or sale, by (B) the total number of Common Shares outstanding
         immediately after such issue or sale; and

                  (2) by multiplying the Per Share Warrant Price in effect
         immediately prior to the time of such issue or sale by a fraction, the
         numerator of which shall be (A) the sum of (i) the number of Common
         Shares outstanding immediately prior to such issue or sale multiplied
         by the market price immediately prior to such issue or sale; and (ii)
         the consideration received by the Company upon such sale, divided by
         (B) the total number of Common Shares outstanding immediately after
         such issue or sale, and the denominator of which shall be the market
         price immediately prior to such issue or sale.

         4. Fully Paid Shares; Taxes. The Company agrees that the Common Shares
represented by each and every certificate for Warrant Shares delivered on the
exercise of this Warrant shall, at the time of such delivery, be validly issued
and outstanding, fully paid and non-assessable. The Company further covenants
and agrees that it will pay, when due and payable, any and all Federal and state
stamp, original issue or similar taxes which may be payable in respect of the
issue of any Warrant Share or certificate therefor.

                                       3
<PAGE>   12
         5. Transferability. This Warrant and the Warrant Shares shall not be
sold, transferred, assigned or hypothecated by the Holder except (i) pursuant to
an effective registration statement under the Securities Act of 1933, as
amended, and qualification for sale under all other applicable state and
provincial securities rules and regulations [collectively the "Securities
Acts"]; or (ii) in full compliance with all requirements necessary to establish
an exemption from the registration requirements of the Securities Acts. In order
to properly establish compliance with (ii), above, the Company shall be entitled
to request and receive in advance of authorizing any sale, transfer, assignment
or hypothecation of this Warrant or any of the Warrant Shares: (x) appropriate
transferor and tranferee representation letters supporting a claimed exemption
from registration requirements of the Securities Acts; (y) an opinion of counsel
for the holder of the Warrant and/or Warrant Shares reasonably satisfactory to
the Company that the proposed transfer from the holder of the Warrant and/or
Warrant Shares to the transferee is exempt from the registration requirements of
the Securities Act; and (z) such other documentation, representations and
filings as may be reasonably required by counsel in order to issue the foregoing
opinion. The Company may treat the registered holder of this Warrant as it
appears on the Company's books at any time as the Holder for all purposes.

         6. Loss, etc. of Warrant. Upon receipt of evidence satisfactory to the
Company of the loss, theft, destruction or mutilation of this Warrant, and of
indemnity reasonably satisfactory to the Company, if lost, stolen or destroyed,
and upon surrender and cancellation of this Warrant, if mutilated, and upon
reimbursement of the Company's reasonable incidental expenses, the Company shall
execute and deliver to the Holder a new Warrant of like date, tenor and
denomination.

         7. Warrant Holder Not Shareholder. Except as otherwise provided herein,
this Warrant does not confer upon the Holder any right to vote or to consent or
to receive notice as a shareholder of the Company, as such, in respect of any
matters whatsoever, or any other rights or liabilities as a shareholder, prior
to the exercise hereof.

         8. Communication. No notice or other communication under this Warrant
shall be effective unless, but any notice or other communication shall be
effective and shall be deemed to have been given if, the same is in writing and
is mailed by first-class mail, postage prepaid, addressed to:

         (a) the Company at North American Vaccine, Inc., 10150 Old Columbia
Road, Columbia, MD 21046 Attention: Vice President-Finance, or such other
address as the Company has designated in writing to the Holder, or

         (b) the Holder at BioChem Pharma Inc., 275 Armand Frappier Boulevard,
Laval, H7V 4A7 Quebec, Canada Attention: Executive Vice President-Investments &
Subsidiaries, or such other address as the Holder has designated in writing to
the Company.

                                       4
<PAGE>   13
         9. Headings. The headings of this Warrant have been inserted as a
matter of convenience and shall not affect the construction hereof.

         10. Applicable Law. This Warrant shall be governed by and construed in
accordance with the laws of the State of New York.


                                       5
<PAGE>   14
         IN WITNESS WHEREOF, NORTH AMERICAN VACCINE, INC. has caused this
Warrant to be signed by its Chief Executive Officer and President and its
corporate seal to be hereunto affixed and attested by its Secretary this ____
day of July 1999.

ATTEST:                                 NORTH AMERICAN VACCINE, INC.



_____________________________           By: ____________________________________
[Corporate Seal]                            Randal Chase
                                            Chief Executive Officer & President


                                       6

<PAGE>   1
                                                  [RECYCLE LOGO] Form 813 (8-95)


                     SURETYSHIP AND SUBORDINATION OF CLAIMS


TO: ROYAL BANK OF CANADA

SURETYSHIP

(a)  OBLIGATIONS GUARANTEED

The undersigned and each of them (if more than one) (the "Guarantor", and
collectively the "Guarantors"), guarantees payment on demand to Royal Bank of
Canada (the "Bank") of all debts and obligations, present or future, direct or
indirect, conditional or unconditional, matured or not, which

          VACCINS NORD--AMERICAINS INC. / NORTH AMERICAN VACCINE, INC.
- ------------------------------------------------------------------------------

- ------------------------------------------------------------------------------

(the "Client") may owe to the Bank at any time whatsoever, whether such debts
and obligations

        --  result from agreements or transactions

            --  between the Bank and the Client, or

            --  between the Client and a third party but through which the Bank
                may become the Client's creditor,

        --  or arise in any other manner,

in the country in which this suretyship is given or elsewhere, whether the
Client is bound alone or with others, as principal debtor or as guarantor.

Such debts and obligations of the Client are hereinafter referred to as the
"Obligations".

(b)  AMOUNT OF THE SURETYSHIP

The Guarantor's liability, or if several Guarantors their total liability, under
this suretyship shall be limited to an amount of  SIX MILLION US DOLLARS
                                                -------------------------------
(US $6,000,000.00) dollars plus interest from the date the Bank makes a demand
- ------------------
for payment from a Guarantor at the US Base Rate* plus 2.65% percent per annum
                                                 ------------
both before and after judgment.

"US Base Rate" means the annual rate of interest announced from time to time by
the Bank as a reference rate in effect for determining the interest rates
applicable to US dollar commercial loans made in Canada.

*Insert the rate over Prime, or, in the case of a fixed rate, delete the words
"the Bank's Prime Rate plus" and insert the applicable rate.

SUBORDINATION OF CLAIMS

Each Guarantor subordinates its claims, present and future, against the Client
to the Obligations, so as to enable the Bank in all circumstances to be fully
paid the Obligations in priority over such claims. Any payment received by a
Guarantor with respect to such claims shall be received on behalf of the Bank
and shall be remitted to the Bank immediately. Such remittance shall not
constitute a full or partial discharge of the liability of any Guarantor
hereunder.

This subordination is independent of the suretyship hereunder and shall remain
in effect notwithstanding the termination of the suretyship with respect to one
or more Guarantors.


                                      -1-
<PAGE>   2
GENERAL PROVISIONS

1. SOLIDARY LIABILITY

   1.1 BETWEEN THE CLIENT AND THE GUARANTORS

       The Obligations of the Client and the undertakings of each Guarantor
       hereunder toward the Bank shall be solidary.

   1.2 BETWEEN THE GUARANTORS

       If there is more than one Guarantor, their undertaking hereunder shall be
       solidary.

2. RIGHTS OF THE BANK

   2.1 TRANSACTIONS WITH THE CLIENT AND WITH THIRD PARTIES

       The Bank may grant to the Client or to third parties, including to
       another Guarantor who is a signatory to this or another suretyship,
       delays for performance, renewals, prorogations, extensions of time,
       releases and discharges; the Bank may accept from them security,
       including other suretyships; it may surrender to them all or part of such
       security, including that currently existing; it may abstain from taking
       security or from realizing thereon; it may cease or abstain from granting
       them credit, loans or advances; it may make compromises and deal with
       them and surrender any security; the whole as the Bank may deem
       appropriate, without having to obtain consent from any Guarantor and
       without diminishing or modifying its liability under this agreement.

       Loss of any security held by the Bank from the Client or from third
       parties, whether it results from an act or an omission by the Bank or
       otherwise, shall not diminish nor modify the liability of any Guarantor
       under this agreement.

   2.2 IMPUTATION OF MONIES RECEIVED

       The Bank may apply any payment it receives and any product of realization
       on security it holds to the portion of the Obligations it deems
       appropriate, including the portion which is not guaranteed by this
       suretyship; it may also, at its discretion, change such application; the
       whole without diminishing the liability of any Guarantor under this
       agreement.

3. CONTINUOUS SURETYSHIP

   This suretyship is continuous. It shall subsist notwithstanding the total or
   partial discharge of the Obligations from time to time. It secures the
   ultimate balance owing to the Bank by the Client.

4. RENUNCIATION TO BENEFIT OF DISCUSSION

   Each Guarantor renounces to the benefit of discussion; thus, the Bank shall
   not be obliged to exercise its remedies against the Client or against the
   Client's property before seeking performance of the Obligations of a
   Guarantor hereunder.

5. RENUNCIATION TO BENEFIT OF DIVISION

   Each Guarantor renounces to the benefit of division; thus, the Bank will not
   be obliged to divide its action nor to reduce it to the amount of the share
   of each Guarantor when exercising its rights pursuant to this suretyship.

6. TERMINATION OF THE SURETYSHIP

   6.1 REVOCATION

       Each Guarantor may, by written notice to the manager of the branch or
       agency of the Bank which has received this suretyship agreement,
       terminate its liability under this suretyship with respect to future
       Obligations, but not with respect to the Obligations existing on the date
       of receipt of such notice, even if such Obligations are not exigible at
       such time; furthermore, notwithstanding the receipt of such notice, the
       Bank has the right to comply with the demands of the Client based on
       express or tacit agreements entered into prior to the receipt of such
       notice and any Obligation resulting therefrom shall be covered by this
       suretyship.

   6.2 DEATH

       The death of a Guarantor shall terminate this suretyship and the
       liability of the Guarantor's succession for future Obligations, but shall
       not terminate it with respect to the Obligations existing on the date on
       which the death occurred, even if such Obligations are not exigible at
       such time; furthermore, notwithstanding the death, the Bank has the right
       to comply with the demands of the Client based on express or tacit
       agreements entered into prior to the occurrence of the death, and any
       Obligation resulting therefrom shall be covered by this suretyship.

   6.3 EFFECT ON OTHER GUARANTORS

       In the event this suretyship is terminated with respect to one or several
       Guarantors, for a reason stated hereinabove or otherwise, it shall remain
       in effect for the remaining Guarantors.

7. NON-DISCHARGING EVENTS

   7.1 GENERAL

       This suretyship and this subordination agreement shall remain in effect
       notwithstanding:

       - the change of name of the Client,

       - the merger of the Client with another legal person,

       - if the Client is a partnership, a change in its composition, business
         or purpose,

       - if the Client is a legal person, a change in its purpose, capital
         structure, charter or business

       The term "Client" shall then be deemed to include, for the purposes of
       this agreement, such new name, the legal person resulting from such
       merger, or such partnership or legal person so modified.

   7.2 SURETYSHIP ATTACHED TO THE PERFORMANCE OF DUTIES

       If this suretyship is attached to the performance of special duties of
       any Guarantor, termination of such duties shall not have the effect of
       terminating this suretyship.

   7.3 INCAPACITY OF THE CLIENT

       The Obligations are guaranteed by this suretyship notwithstanding any
       incapacity or inability of the Client or of its directors, partners or
       agents, or the absence of juridical personality of the Client, or the
       fact that legal action cannot be brought against the Client, or any
       irregularity or defect in the formation of the Obligations, whether or
       not the Bank is aware of it.

8. POSTPONEMENT OF SUBROGATION

   Each Guarantor agrees to refrain from exercising its right of subrogation
   until the Bank receives full payment of the Obligations.

9. INDEPENDENCE OF THE SURETYSHIP

   This suretyship is in addition to all other suretyships and undertakings
   given or made by whomsoever to the Bank with regard to the Client. However,
   it is in substitution for any suretyship surrendered by the Bank in
   consideration of establishing this suretyship.

10. STATEMENTS OF ACCOUNT

   Any statement prepared by the Bank shall be accepted by the Guarantors as
   conclusive evidence of the amount owing by the Client to the Bank on the date
   of such statement.

11. EFFECTIVE DATE

   This agreement is binding upon all its signatories, even if one or more
   intended signatories did not execute it.

   The possession by the Bank of this agreement constitutes conclusive evidence
   that the latter was not delivered on the understanding that it would only
   come into effect after certain prior or subsequent conditions were met
   unless, at the time the Bank takes delivery of it, each of the signatories
   obtains from the manager of the branch or agency of the Bank taking delivery
   of this agreement a letter establishing the conditions pursuant to which it
   was delivered and, if applicable, those which must be complied with prior to
   the agreement taking effect.

12. DEMAND FOR PAYMENT

   A demand for payment shall be deemed to have been made to any Guarantor when
   a stamped envelope containing such demand and addressed to such Guarantor is
   mailed to the latter's last address known to the Bank.

   In the event that a Guarantor dies, a demand for payment mailed as aforesaid
   and addressed to any one of the heirs, executors, liquidators, administrators
   or legal representatives of such Guarantor at the last address of the
   deceased Guarantor known to the Bank, shall be deemed to have been made to
   all of them.

   When it deems it necessary for the protection of its interests, the Bank may
   avail itself of its rights resulting from this suretyship without being
   required to make a prior demand for payment.

13. PLACE OF PAYMENT

   All payments hereunder shall be made to the Bank, at one of its branches or
   agencies.



                                      -3-

<PAGE>   3
14. ENTIRE AGREEMENT

    7. NON-DISCHARGING EVENTS

       7.1 GENERAL

           This suretyship and this subordination agreement shall remain in
           effect notwithstanding:

           - the change of name of the Client,

           - the merger of the Client with another legal person,

           - if the Client is a partnership, a change in its composition,
             business or purpose,

           - if the Client is a legal person, a change in its purpose, capital
             structure, charter or business.

           The term "Client" shall then be deemed to include, for the purposes
           of this agreement, such new name, the legal person resulting from
           such merger, or such partnership or legal person so modified.

       7.2 SURETYSHIP ATTACHED TO THE PERFORMANCE OF DUTIES

           If this suretyship is attached to the performance of special duties
           of any Guarantor, termination of such duties shall not have the
           effect of terminating this suretyship.

       7.3 INCAPACITY OF THE CLIENT

           The Obligations are guaranteed by this suretyship notwithstanding any
           incapacity or inability of the Client or of its directors, partners
           or agents, or the absence of juridical personality of the Client, or
           the fact that legal action cannot be brought against the Client, or
           any irregularity or defect in the formation of the Obligations,
           whether or not the Bank is aware of it.

   8. POSTPONEMENT OF SUBROGATION

      Each Guarantor agrees to refrain from exercising its right of subrogation
      until the Bank receives full payment of the Obligations.

   9. INDEPENDENCE OF THE SURETYSHIP

      This suretyship is in addition to all other suretyships and undertakings
      given or made by whomsoever to the Bank with regard to the Client.
      However, it is in substitution for any suretyship surrendered by the Bank
      in consideration of establishing this suretyship.

  10. STATEMENTS OF ACCOUNT

      Any statement prepared by the Bank shall be accepted by the Guarantors as
      conclusive evidence of the amount owing by the Client to the Bank on the
      date of such statement.

  11. EFFECTIVE DATE

      This agreement is binding upon all its signatories, even if one or more
      intended signatories did not execute it.

      The possession by the Bank of this agreement constitutes conclusive
      evidence that the latter was not delivered on the understanding that it
      would only come into effect after certain prior or subsequent conditions
      were met unless, at the time the Bank takes delivery of it, each of the
      signatories obtains from the manager of the branch or agency of the Bank
      taking delivery of this agreement a letter establishing the conditions
      pursuant to which it was delivered and, if applicable, those which must be
      complied with prior to the agreement taking effect.

  12. DEMAND FOR PAYMENT

      A demand for payment shall be deemed to have been made to any Guarantor
      when a stamped envelope containing such demand and addressed to such
      Guarantor is mailed to the latter's last address known to the Bank.

      In the event that a Guarantor dies, a demand for payment mailed as
      aforesaid and addressed to any one of the heirs, executors, liquidators,
      administrators or local representatives of such Guarantor at the last
      address of the deceased Guarantor known to the Bank, shall be deemed to
      have been made to all of them.

      When it deems it necessary for the protection of its interests, the Bank
      may avail itself of its rights resulting from this suretyship without
      being required to make a prior demand for payment.

  13. PLACE OF PAYMENT

      All payments hereunder shall be made to the Bank, at one of its branches
      or agencies.


                                      -3-


<PAGE>   1
                                                                    Exhibit 4.A

SHARE PURCHASE AGREEMENT entered into in the Province of Quebec this 17th day of
January, 1990.

<TABLE>
<S>                                         <C>
BY AND BETWEEN:                             NORTH AMERICAN VACCINE, INC., a
                                            corporation duly existing under the
                                            Canada Business Corporations Act,
                                            having its head office in the
                                            Montreal Urban Community, Quebec

                                            (hereinafter referred to as "NAVA")

                                            PARTY OF THE FIRST PART

AND:                                        IAF BIOCHEM INTERNATIONAL INC., a
                                            corporation duly existing under
                                            Part 1A of the Quebec Companies
                                            Act, having its head office in the
                                            City of Laval, Quebec

                                            (hereinafter referred to as "BioChem")

                                            PARTY OF THE SECOND PART
</TABLE>

        WHEREAS NAVA has been duly constituted and has a valid existence under
the provisions of the Canada Business Corporations Act and will directly or
through its subsidiaries, engage in the research, development, manufacturing
and marketing of human immuno-biological products;

        WHEREAS the offering of approximately 9,034,412 common shares of NAVA
will be registered under the provisions of the United States Securities Act of
1933;

        WHEREAS approximately 13,735,399 common shares of NAVA will be approved
for listing on the American Stock Exchange ("AMEX");


<PAGE>   2
                                      -2-

        WHEREAS BioChem is desirous of subscribing for approximately four
million five hundred and seventeen thousand two hundred and six (4,517,206)
common shares (the "Common Shares") and one million (1,000,000) Series A
preferred shares (the "Preferred Shares") in the share capital of NAVA,
issuable from the treasury of NAVA, (hereinafter collectively referred to as
the "Shares"), and certain options, warrants or other rights to acquire
additional shares of NAVA (the "Options"), the whole on the terms and
conditions hereinafter set out;

        WHEREAS the consideration for the issuance of the Shares and the
Options is i) the sum of five million dollars in lawful currency of the United
States (U.S. $5,000,000) payable by wire transfer of immediately available U.S.
funds by BioChem to NAVA on the Closing Date, ii) the issuance by BioChem on
the Closing Date of four hundred ninety eight thousand nine hundred eighty four
(498,984) common shares of Biochem and iii) the transfer by BioChem to NAVA of
certain technology and other interests, pursuant to the Technology Transfer
Agreement, (i), ii) and iii) are hereinafter referred to as the "Purchase
Price"), the whole on the terms and conditions hereinafter set out;

        WHEREAS NAVA is desirous of issuing the Shares and Options to BioChem
in the numbers and for the Purchase Price as aforesaid, the whole subject to
the terms and conditions hereinafter set forth:

         NOW, THEREFORE, THE PARTIES HERETO AGREE AS FOLLOWS:

                                  SECTION ONE

                                 INTERPRETATION

1.1     Definitions:  -  Unless the subject matter or context otherwise
        requires:

        (a)    "American Vaccine" means American Vaccine Corporation, a
               corporation incorporated under the laws of Delaware.

        (b)    "AMVAX" means Amvax, Inc., a wholly-owned subsidiary of American
               Vaccine incorporated under the laws of Delaware.

        (c)    "Agreement" means this Agreement and any instrument supplemental
               or ancillary hereto;


<PAGE>   3


                                      -3-

               and the expressions "recital", "Article", "section",
               "subsection", "paragraph" and "subparagraph" followed by a
               number or letter or combination thereof mean and refer to the
               specified recital, Article, section, subsection, paragraph or
               subparagraph of this Agreement.

        (d)    "American Vaccine Financial Statements" means the audited
               financial statements of American Vaccine on a consolidated basis
               as of and for the period ended December 31, 1988.

        (e)    "American Vaccine Unaudited Financial Statements" means the
               unaudited financial statements of American Vaccine on a
               consolidated basis as of and for the period ended June 30, 1989.

        (f)    "Assignment and Amendment Agreement" means the agreement made as
               of January 9, 1990 among CPDL, BioChem and NAVA pursuant to
               which the CPDL Agreements are assigned to NAVA.

        (g)    "BioChem Common Shares" means the four hundred and ninety eight
               thousand nine hundred eighty four (498,984) common shares of
               BioChem to be issued to NAVA as part of the Purchase Price.

        (h)    "BioChem Financial Statements" means the audited financial
               statements of BioChem as of and for the period ended January 31,
               1989.

        (i)    "BioChem Unaudited Financial Statements" means the unaudited
               financial statements of BioChem as of and for the period ended
               July 31, 1989.

        (j)    "Closing" means the completion of all procedures and the
               delivery of all documents and opinions required to consummate
               the transactions contemplated herein and the payment of the
               Purchase Price; and "Closing Date" means the date specified in
               section 3.1 on which the Closing shall occur.

        (k)    "Common Shares" means the approximately 4,517,206 common shares,
               no par value, of the share capital of NAVA to be issued to
               BioChem.


<PAGE>   4
                                      -4-

        (l)    "CPDL" means Canadian Patents and Development Limited.

        (m)    "CPDL Agreements" means the agreements entered into between
               BioChem and the Canadian Patents Development Limited dated July
               27, 1987 and June 27, 1988 respectively.

        (n)    "The Frost Group" means Frost-Nevada Limited Partnership, IVAX
               Corporation and Dr. Phillip Frost.

        (o)    "IAF Vaccines" means the corporation to be formed in the event
               that the IAF Vaccines Transaction is completed and of which
               BioChem will hold all of the voting equity.

        (p)    "IAF Vaccines Transaction" means the proposed acquisition of the
               vaccine division of Institut Armand-Frappier by IAF Vaccines
               pursuant to the terms of the memorandum of agreement entered
               into between Institut Armand-Frappier and BioChem dated December
               21, 1989.

        (q)    "NAVA Merger Sub" means NAVA Acquiring Corp., a wholly-owned
               subsidiary of NAVA incorporated under the laws of Delaware.

        (r)    "NTIS" means the National Technical Information Service, a
               primary operating unit of the United States Department of
               Commerce.

        (s)    "NTIS Agreement" means the License Agreement entered into
               between Selcore Laboratories, Inc. (the predecessor of American
               Vaccine) and NTIS on March 25, 1988.

        (t)    "Options" means such options and warrants of NAVA as will permit
               BioChem to maintain its 50% fully diluted ownership as of the
               Closing Date of the issued and outstanding Common Shares of NAVA
               after giving effect to the transactions contemplated by this
               Agreement, the terms of which are described in Schedule 1
               hereto.

        (u)    "Preferred Shares" means the one million (1,000,000) Series A
               Preferred Shares, no par value, of the share capital of NAVA to
               be issued to BioChem on the Closing Date.


<PAGE>   5

                                      -5-
        (v)    "Pertussis Technology" means the inventions commonly known as
               methods of preparing toxoid and fermentation level cultivation
               of Bordetella pertussis and all technical knowledge and
               techniques relating generally to the inventions and which
               inventions, technical knowledge and techniques are the subject
               of the NTIS Agreement and the Sekura Agreement.

        (w)    "Purchase Price" means i) the sum of five million dollars in
               lawful currency of the United States (US $5,000,000) payable by
               wire transfer of immediately available U.S. funds by BioChem to
               NAVA on the Closing Date, ii) the BioChem Common Shares and iii)
               certain technology and other interests to be transferred on the
               Closing Date by BioChem to NAVA pursuant to the Technology
               Transfer Agreement.

        (x)    "Registration Statement" means the preliminary registration
               statement on Form S-4 as filed with the Securities and Exchange
               Commission by NAVA on October 17, 1989 and all exhibits and
               amendments thereto, including without limitation, the Annual
               Report of American Vaccine on Form 10-K for the year ended
               December 31, 1988 and the Quarterly Reports on Form 10-Q of
               American Vaccine for the quarters ended March 31, 1989 and June
               30, 1989.

        (y)    "Reorganization" means the merger of NAVA Merger Sub with and
               into American Vaccine as described in the Registration
               Statement.

        (z)    "Sekura Agreement" means the Amended and Restated Pertussis
               Vaccine Patent License Agreement entered into between Selcore
               Laboratories, Inc. (the predecessor of American Vaccine) and
               Ronald D. Sekura on October 13, 1987.

        (aa)   "Shareholders' Agreement" means the agreement dated January 17,
               1990 among BioChem and The Frost Group in substantially the form
               of Schedule 2 hereto.

        (ab)   "Shares" means the Common Shares and Preferred Shares.

        (ac)   "Technology Transfer Agreement" means the agreement dated
               January 17, 1990 between BioChem and NAVA and substantially in
               the form of Schedule 3 hereto.


<PAGE>   6

                                      -6-

1.2     Schedules: The following Schedules attached or referred to in this
        Agreement are an integral part of this Agreement:

               Schedule 1  - Terms of the Options
               Schedule 2  - Form of Shareholders' Agreement
               Schedule 3  - Form of Technology Transfer Agreement
               Schedule 4  - Registration Rights

1.3     Extended Meanings:   -   Words importing the singular number include
        the plural and vice versa and words importing the masculine gender
        include the feminine and neuter genders.

1.4     Interpretation Not Affected by Headings: - The division of this
        Agreement into sections and the insertion of headings are for
        convenience of reference only and shall not affect the construction or
        interpretation of this Agreement.

1.5     Applicable Law: - This Agreement shall be deemed to have been made in
        the Province of Quebec and shall be interpreted in accordance with and
        be governed by the laws of Quebec and the laws of Canada applicable
        therein.

1.6     Funds: - All dollar amounts referred to in this Agreement are in lawful
        money of the United States, unless otherwise stated.

1.7     Paramountcy: - If any provision of this Agreement conflicts with the
        incorporating documents or any by-law of NAVA, American Vaccine or
        AMVAX, the provisions of this Agreement shall prevail to the extent
        permitted by law.

1.8     Severability: - In the event that any provision or provisions of this
        Agreement is or are illegal under the laws of the Province of Quebec,
        then such provision or provisions shall be deemed not to have been
        written into this Agreement and the remaining terms and provisions
        thereof shall subsist and remain enforceable. Upon the determination
        that any such provision is invalid, illegal or unenforceable, the
        parties hereto shall negotiate in good faith to modify this Agreement
        so as to effect the original intent of the parties as closely as
        possible in order that the transactions contemplated hereby are
        fulfilled to the extent possible.


<PAGE>   7
                                      -7-

1.9     Business Day: - In the event that any action to be taken hereunder
        falls on a Saturday, Sunday or any legal holiday ("non-business day")
        either in Canada or the United States, then such action shall be taken
        on the next succeeding day other than a non-business day.

                                  SECTION TWO

                                  SUBSCRIPTION

2.1     Subscription for Shares: Subject to the terms and conditions hereof,
        BioChem agrees to purchase, on the Closing Date, approximately four
        million five hundred seventeen thousand two hundred six (4,517,206)
        Common Shares of NAVA, one million (1,000,000) Series A Preferred
        Shares of NAVA and Options to acquire approximately one million one
        hundred ninety two thousand seven hundred ninety nine (1,192,799)
        Common Shares of NAVA for an aggregate consideration equal to the
        Purchase Price.

2.2     Exercise of Options:

        (a) Schedule 1 hereto sets forth certain information concerning the
        options and warrants of NAVA (the "NAVA Options") granted to the
        holders specified in Schedule 1. NAVA shall have the right, by action
        of the Board of Directors, at any time and from time to time, to change
        any of the terms of the NAVA Options set forth in Schedule 1. Any
        reference in this Agreement to "the terms set forth in Schedule 1"
        shall refer to the terms of the NAVA Options as they may be changed
        from time to time by action of the NAVA Board of Directors.

        (b) BioChem may exercise its Options in accordance with the terms set
        forth in Schedule 1 with respect to the corresponding NAVA Options only
        if and to the extent that any holder thereof exercises its NAVA Options
        and for the same number of NAVA common shares for which such Options
        are exercised. The Options shall lapse and be of no further legal
        effect as, when and to the extent that the corresponding NAVA Options
        lapse and become without legal effect.

        (c) Within five (5) business days following the exercise of any NAVA
        Options, NAVA shall furnish BioChem with a written notice of such
        exercise specifying (i) the number of common shares of NAVA


<PAGE>   8
                                      -8-

        issued upon the exercise of such NAVA Options, (ii) the purchase price
        paid to NAVA for such common shares, (iii) the expiry date of such NAVA
        Options and (iv) such other information concerning such exercise of
        NAVA Options as NAVA shall deem appropriate. BioChem shall have the
        right to exercise such number of Options as shall result in the
        issuance to BioChem of the same number of common shares as were issued
        to the holder or holders of the NAVA Options exercised as described
        above by paying in cash the purchase price of the common shares by the
        later of 90 days from receipt of such notice or the expiry date of such
        NAVA Options.

2.3     Allocation: The parties agree to allocate the amount of the Purchase
        Price as follows:

        (i)    as to the Options the sum of U.S. $3,382,062;
        (ii)   as to the Preferred Shares: (a) the sum of U.S. $1,617,938, and
               (b) 463,206.2 of the BioChem Common Shares;
        (iii)  as to the Common Shares: (a) 35,777.8 of the BioChem Common
               Shares, and (b) the interests to be transferred by BioChem to
               NAVA pursuant to Section 2 of the Technology Transfer Agreement.

        The parties shall jointly elect under the provisions of the Income Tax
Act (Canada) and the Quebec Taxation Act that BioChem's proceeds of disposition
of the intangible consideration and NAVA's cost of the intangible consideration
shall be an amount equal to the adjusted cost base of the intangible
consideration to BioChem. The parties further agree to jointly make the
necessary elections and to execute and file the prescribed election forms and
any other documents required pursuant to section 85 of the Income Tax Act
(Canada) and the corresponding sections of the Taxation Act (Quebec) and any
regulations under such Acts.

                                 SECTION THREE

                                     CLOSING

3.1     Closing Date: The Closing of the purchase by BioChem of the Shares and
        Options shall take place at the offices of Stikeman, Elliott at 1155
        Rene-Levesque Blvd., West, Suite 3900, Montreal, Quebec on February 27,
        1990 at 10:00 a.m. or such other date, time or place as the parties
        hereto may mutually agree but in no event


<PAGE>   9
                                      -9-

        prior to the filing of a Certificate of Merger with the Office of the
        Secretary of State of the State of Delaware with respect to the
        consummation of the Reorganization.

3.2     Conditions of Closing in favour of BioChem: The obligation of BioChem
        to purchase the Shares and the Options as contemplated under Section 2
        hereof and to perform its other obligations hereunder is subject to (i)
        the simultaneous completion of the Reorganization, and (ii) the
        fulfillment of the following conditions precedent being satisfied on or
        prior to the Closing Date, it being understood that the said conditions
        are for the exclusive benefit of BioChem and may be waived in writing,
        in whole or in part, by BioChem at any time prior to the Closing Date:

        (a)    the common shares of NAVA shall be listed or approved for
               listing on AMEX;

        (b)    the representations and warranties contained in Section 4.1
               hereof shall be true, correct and complete in all material
               respects on and as of the date made and on the Closing Date and
               on the Closing Date NAVA shall deliver a certificate confirming
               the foregoing in form and substance satisfactory to BioChem;

        (c)    the Shareholders' Agreement shall have been executed and
               delivered by all parties thereto;

        (d)    except as disclosed in the Registration Statement i) no action,
               suit or proceeding against NAVA, American Vaccine or AMVAX shall
               have been instituted or threatened before or by any U.S.,
               Canadian or other court or tribunal or governmental agency or
               other regulatory or administrative agency or commission or other
               third party, and no legislation, rule or regulation shall have
               been proposed, implemented or enacted which action, suit,
               proceeding or legislation, rule or regulation seeks to restrain
               or prohibit or otherwise challenge the legality or validity of
               the transactions contemplated hereby or of the Reorganization
               and ii) no material adverse change in (or any condition or event
               which would have a material adverse effect on) the business,
               assets, capitalization or financial condition of American
               Vaccine on a consolidated basis since June 30, 1989 shall have
               occurred;


<PAGE>   10

                                      -10-

        (e)    all orders, exemptions and rulings from applicable regulatory
               authorities where such are required to be obtained shall have
               been received;

        (f)    counsel to BioChem shall have delivered to BioChem an opinion
               confirming that the transactions contemplated hereby do not
               result in any material adverse Canadian income tax consequences
               for BioChem;

        (g)    all proceedings shall have been taken by NAVA and American
               Vaccine in accordance with applicable law as are required to
               complete the transactions contemplated hereby including
               completion of the Reorganization;

        (h)    the Board of Directors of American Vaccine and NAVA, as the case
               may be, shall have approved the purchase by BioChem of the
               Shares and the options and the shareholders of American Vaccine
               shall have approved the Reorganization and American Vaccine and
               NAVA, as the case may be, shall have provided BioChem with
               certified copies of resolutions duly adopted by its Board of
               Directors in connection with the foregoing;

        (i)    BioChem shall have received legal opinions in form and substance
               satisfactory to it from Stikeman, Elliott and from Shaw,
               Pittman, Potts & Trowbridge;

        (j)    NAVA shall have delivered to BioChem one or more certificates,
               duly registered in the name of BioChem, representing the Common
               Shares and Preferred Shares purchased by it, and such agreements
               and instruments as shall be necessary to issue or vest title to
               the Options in BioChem;

        (k)    all documents shall have been executed in a manner that is
               satisfactory in form and substance to BioChem;

        (l)    BioChem shall have obtained all consents, amendments and
               modifications to any agreements or other documents which are
               required in order to consummate, validly and enforceably, the
               transactions contemplated herein.


<PAGE>   11

                                      -11-

3.3     Conditions of Closing in favour of NAVA: The obligation of NAVA to sell
        the Shares and the Options as contemplated under Section 2 hereof and
        to perform its other obligations hereunder is subject to the following
        conditions precedent being satisfied on or prior to the Closing Date,
        it being understood that the said conditions are for the exclusive
        benefit of NAVA and may be waived in whole or in part by NAVA at any
        time prior to the Closing Date:

        (a)    the representations and warranties contained in Section 4.2
               hereof shall be true, correct and complete in all material
               respects on and as of the date made and on the Closing Date and
               on the Closing Date BioChem shall deliver a certificate
               confirming the foregoing in form and substance satisfactory to
               NAVA and counsel to NAVA;

        (b)    (i) no action, suit or proceeding against NAVA, BioChem,
               American Vaccine or AMVAX shall have been instituted or
               threatened before or by any U.S., Canadian or other court or
               tribunal or governmental agency or other regulatory or
               administrative agency or commission or other third party, and no
               legislation, rule or regulation shall have been proposed,
               implemented or enacted which action, suit, proceeding or
               legislation, rule or regulation seeks to restrain or prohibit or
               otherwise challenge the legality or validity of the transactions
               contemplated hereby and (ii) no material adverse change in (or
               any condition or event which would have a material adverse
               effect on) the business, assets, capitalization or financial
               condition of BioChem since July 31, 1989 shall have occurred
               (except any change resulting from the IAF Vaccines Transaction
               or the financing thereof or the acquisition of voting rights by
               the holders of the BioChem Preferred Shares in accordance with
               the terms currently attached to such shares, it being
               understood, in this latter case, that the occurrence of any
               change that gives rise to the acquisition of such voting rights
               is not an excepted material adverse change for the purposes
               hereof);

        (c)    all orders, exemptions and rulings from applicable regulatory
               authorities where such are required to be obtained shall have
               been received;


<PAGE>   12
                                      -12-

        (d)    Shaw, Pittman, Potts & Trowbridge shall have delivered to
               American Vaccine an opinion confirming that the transactions
               contemplated hereby (including the Reorganization) will not
               result in any material adverse income tax consequences for
               American Vaccine;

        (e)    all proceedings shall have been taken by BioChem in accordance
               with applicable law as are required to complete the transactions
               contemplated hereby;

        (f)    the Board of Directors of BioChem shall have approved the
               transactions contemplated hereby and BioChem shall have
               furnished NAVA with certified copies of resolutions duly adopted
               by its Board of Directors in connection with the foregoing;

        (g)    NAVA shall have received a legal opinion in form and substance
               satisfactory to it from Stikeman, Elliott;

        (h)    Bear, Stearns & Co., Inc. ("Bear Stearns") shall have delivered
               to the Board of Directors of American Vaccine an opinion as to
               the fairness of the purchase by BioChem of the Shares and the
               Options and of the Reorganization to the American Vaccine
               Stockholders from a financial point of view;

        (i)    BioChem shall have executed and delivered the Technology
               Transfer Agreement and the Assignment and Amendment Agreement;

        (j)    BioChem shall have paid the cash portion of the Purchase Price,
               shall have delivered to NAVA one or more share certificates duly
               registered in the name of NAVA representing the Biochem Common
               Shares and shall have transferred certain technology and other
               interests to NAVA pursuant to the Technology Transfer Agreement;

        (k)    the Shareholders' Agreement shall have been executed and
               delivered by all parties thereto;

        (l)    all documents shall have been executed in a manner that is
               satisfactory in form and substance to NAVA;

        (m)    American Vaccine and AMVAX shall have obtained all consents,
               amendments and modifications to any


<PAGE>   13

                                      -13-

               agreements or other documents which are required in order to
               consummate, validly and enforceably, the transactions
               contemplated herein;

                                  SECTION FOUR

                         REPRESENTATIONS AND WARRANTIES

4.1     Representations and Warranties of NAVA: NAVA represents and warrants,
        for itself and American Vaccine and AMVAX, to BioChem as follows:

        (a)    that NAVA, American Vaccine and AMVAX are validly existing
               corporations in good standing under the laws of their
               jurisdictions of incorporation and that each has all necessary
               corporate power to execute and deliver the Agreement and all
               related agreements contemplated hereby and to complete the
               transactions contemplated hereby;

        (b)    that the authorization, execution, delivery or performance by
               NAVA of the Agreement is not in conflict with and does not or
               will not result in a breach or after notice or lapse of time or
               both will not result in a breach of any of the terms or
               provisions of NAVA's articles or by-laws or of the material
               contracts, agreements or undertakings to which it is a party or
               to which it may be subject, as the case may be;

        (c)    the authorized share capital of NAVA consists of an unlimited
               number of common shares and an unlimited number of preferred
               shares issuable in series of which approximately 9,034,412
               common shares and 2,000,000 Series A preferred shares will, on
               the Closing Date, have been duly authorized for issuance and
               sale and when issued and delivered by NAVA pursuant to this
               Agreement and the Agreement and Plan of Merger among NAVA, NAVA
               Merger Sub and American Vaccine dated as of October 25, 1989
               (the "Merger Agreement") against payment of the consideration
               set out in the Agreement and the Merger Agreement, will be
               validly issued and fully paid and non-assessable;

        (d)    the authorized share capital of American Vaccine consists of ten
               million (10,000,000) shares of common stock, $.01 par value per
               share, and two million (2,000,000) shares of preferred stock


<PAGE>   14
                                      -14-

               $.01 par value per share, issuable in series, and all of the
               issued and outstanding capital stock of American Vaccine is
               legally issued and outstanding as fully paid and non-assessable;

        (e)    the authorized share capital of AMVAX consists of 1,000,000
               shares of common stock s.01 par value per share and 250,000
               shares of preferred stock $30.00 par value per share, and all of
               the issued and outstanding capital stock of AMVAX is legally
               issued and outstanding as fully paid and nonassessable;

        (f)    that as of the Closing Date, NAVA will own beneficially all of
               the issued and outstanding shares of American Vaccine which in
               turn as of the Closing Date will own all of the issued and
               outstanding shares of AMVAX, and that each of NAVA, American
               Vaccine and AMVAX is duly licensed, qualified to do business and
               in good standing in all jurisdictions in which they carry on
               their business except where failure to do so does not have a
               material adverse effect on each such corporation respectively;

        (g)    that American Vaccine has no subsidiary, affiliated corporation
               or controlling interest in any partnership, joint venture or
               similar entity except for AMVAX;

        (h)    that AMVAX has no subsidiary, affiliate corporation or
               controlling interest in any partnership, joint venture or
               similar entity;

        (i)    the American Vaccine Financial Statements present fairly in all
               material respects the financial position of American Vaccine on
               a consolidated basis as of December 31, 1988 and the results of
               operations and cash flow for the nine months then ended, in
               conformity with U.S. generally accepted accounting principles;

        (j)    the American Vaccine Unaudited Financial Statements present
               fairly in all material respects the financial position of
               American Vaccine on a consolidated basis as of June 30, 1989 and
               the results of operations and cash flow for the six months then
               ended, in conformity with U.S. generally accepted accounting
               principles;


<PAGE>   15

                                      -15-

        (k)    except as disclosed in the Registration Statement, since June
               30, 1989, there has been no material adverse change to the
               assets, liabilities, or financial position of American Vaccine
               on a consolidated basis other than changes arising in the
               ordinary course of business;

        (l)    that there are no outstanding agreements, options, commitments,
               rights or privileges, preemptive or contractual, giving any
               person the right to purchase or otherwise acquire any securities
               of NAVA, American Vaccine and AMVAX, except for the outstanding
               Series A Preferred Stock of American Vaccine and stock options
               and warrants of American Vaccine as set forth in Schedule 1
               hereto and except as otherwise disclosed in the Agreement;

        (m)    that as of the Closing Date, (i) NAVA and American Vaccine will
               have made all necessary filings with all governmental and
               regulatory authorities, securities commissions and exchanges
               required to effect the transactions contemplated hereby, (ii)
               NAVA, American Vaccine and AMVAX will have duly filed all tax
               returns that are required to have been filed in applicable
               jurisdictions, (iii) each such return is complete, accurate and
               in compliance with applicable law and regulations in all
               material respects, and (iv) each of NAVA, American Vaccine and
               AMVAX will have paid or provided for all such taxes of any
               nature whatsoever, with any related penalties, interest and
               liabilities, that are or would be shown on such tax returns as
               due and payable on or before the Closing Date, other than such
               taxes as are being contested in good faith;

        (n)    that no order suspending or prohibiting the sale or the trading
               of shares or of any securities of NAVA, American Vaccine and
               AMVAX has been issued by any court, securities commission or
               regulatory authority and no proceedings for such purpose are
               pending or, to NAVA's knowledge, threatened;

        (o)    except as disclosed in the Registration Statement and except for
               claims which have been provided for or reserved against in the
               most recent balance sheet of the applicable corporation
               furnished to BioChem, or except as disclosed and


<PAGE>   16
                                      -16-

               accepted by the other party in the Agreement, there are no
               asserted claims or unasserted claims of which NAVA, American
               Vaccine or AMVAX is aware, as it pertains to each corporation,
               against such corporation or any litigation, action, suit or
               other claim by or before any court, tribunal, governmental
               agency or authority, securities commission or regulatory body
               that is material to the business, affairs, property or assets of
               NAVA or American Vaccine on a consolidated basis, as the case
               may be including, without limitation, claims for breach of
               warranty or product liability, claims challenging the ownership
               or use by any such corporation of any material asset and claims
               asserting the invalidity of this Agreement or seeking to prevent
               any of the transactions contemplated hereby;

        (p)    except as disclosed in the Registration Statement, to the best
               of NAVA's knowledge after reasonable investigation, i) the
               Pertussis Technology, including all intellectual property rights
               therein, the use thereof, and the marketing and distribution of
               products produced through such use, do not infringe upon any
               patent, copyright, trade secret or other proprietary right held
               by any third party; (ii) no proceedings have been instituted,
               are pending or threatened which challenge the rights granted to
               American Vaccine under the NTIS Agreement and the Sekura
               Agreement or the validity of NTIS's and/or Ronald D. Sekura's
               intellectual property rights in the Pertussis Technology and
               (iii) none of the patents, copyrights, or other proprietary
               rights of NTIS and Ronald D. Sekura in the Pertussis Technology
               are being infringed upon by others, and none of such rights are
               subject to any outstanding order or judgment;

        (q)    the NTIS Agreement and the Sekura Agreement constitute valid and
               binding contracts enforceable according to their terms;

        (r)    except as disclosed in the Registration Statement, there are no
               pending, or to the best of NAVA's knowledge, after reasonable
               investigation, threatened disputes or controversies with the
               manufacturers, suppliers, customers, consultants and others
               having business


<PAGE>   17
                                      -17-

               relations with NAVA, American Vaccine or AMVAX and each such
               corporation has taken all reasonable security measures to
               protect the secrecy, confidentiality and value of its respective
               proprietary and confidential technology and know-how and, to the
               best of NAVA's knowledge after reasonable investigation, such
               technology and know-how is not in the public domain, nor has it
               been used, divulged, or appropriated for the benefit of any
               person other than such corporations;

        (s)    AMVAX has entered into a valid and enforceable agreement with
               the National Institute of Child Health and Human Development
               ("NICHD") which provides for payments of up to U.S. $3,500,000
               payable for work performed during the period from March 6, 1989
               to March 5, 1990 of which AMVAX has, as of June 30, 1989
               received U.S. $362,704;

        (t)    the Registration Statement does not contain any untrue statement
               of a material fact or omit any material fact required to be
               stated therein or necessary in order to make the statements
               therein not misleading in light of the circumstances under which
               they were made; provided however, that NAVA makes no
               representation or warranty with respect to the information
               contained in or omitted from the Registration Statement
               regarding BioChem or the Institut Armand-Frappier;

        (u)    the representations and warranties contained in this Section 4.1
               shall be true in all material respects on and as of the Closing
               Date with the same force and effect as though such
               representations and warranties had been made on and as of the
               Closing Date and shall survive any investigations by or on
               behalf of BioChem and shall survive the Closing.

4.2     Representations and Warranties of BioChem: BioChem represents and
        warrants to NAVA as follows:

        (a)    that it is a corporation validly incorporated and organized and
               is validly subsisting and in good standing under the laws of its
               jurisdiction of incorporation and that it has all necessary
               corporate power to execute and deliver the Agreement and all
               related agreements contemplated hereby and to complete the
               transactions contemplated hereby;


<PAGE>   18

                                      -18-

        (b)    that none of the authorization, execution, delivery or
               performance by BioChem of the Agreement is in conflict with and
               none of them does or will result in a breach of or does or will
               create a state of facts which after notice or lapse of time or
               both will result in a breach of any of the terms or provisions
               of its articles or by-laws or of the material contracts,
               agreements or undertakings to which BioChem may be a party or
               may be subject, as the case may be;

        (c)    the authorized capital of BioChem consists of an unlimited
               number of common shares and ten million (10,000,000) preferred
               shares having a paid up capital of one hundred thousand dollars
               ($100,000) of which seven million three hundred two thousand one
               hundred sixty five (7,302,165) common shares and ten million
               (10,000,000) preferred shares are legally issued and outstanding
               as fully paid and non-assessable and that on the Closing Date
               the BioChem Common Shares will have been duly authorized for
               issuance and sale to NAVA and will be legally issued and
               outstanding as fully paid and nonassessable;

        (d)    that there are no outstanding agreements, options, commitments,
               rights or privileges, preemptive or contractual, giving any
               person the right to purchase or otherwise acquire any securities
               of BioChem except for stock options and warrants of BioChem for
               an aggregate number of 1,646,451 common shares of BioChem and
               except as otherwise disclosed in the Agreement;

        (e)    the BioChem Financial Statements have been prepared in
               accordance with Canadian generally accepted accounting
               principles applied on a consistent basis and fairly present the
               assets, liabilities and shareholders' equity of BioChem as well
               as its financial position for the period ended on such a day;

        (f)    the BioChem Unaudited Financial Statements have been prepared in
               accordance with Canadian generally accepted accounting
               principles applied on a consistent basis and fairly present the
               assets, liabilities and shareholders' equity of BioChem as well
               as its financial position for the period ended on such a day;


<PAGE>   19
                                      -19-

        (g)    since July 31, 1989, there has been no material adverse change
               to the assets, liabilities, or financial position of BioChem
               other than changes arising in the ordinary course of business;

        (h)    that as of the Closing Date, (i) BioChem will have made all
               necessary filings with all governmental and regulatory
               authorities, securities commissions and exchanges required to
               effect the transactions contemplated hereby, (ii) BioChem will
               have duly filed all tax returns that are required to have been
               filed in applicable jurisdictions, (iii) each such return is
               complete, accurate and in compliance with applicable law and
               regulations in all material respects, and (iv) BioChem will have
               paid or provided for all such taxes of any nature whatsoever,
               with any related penalties, interest and liabilities, that are
               or would be shown on such tax returns as due and payable on or
               before the Closing Date, other than such taxes as are being
               contested in good faith;

        (i)    that no order suspending the sale or the trading of shares or of
               any securities of BioChem has been issued by any court,
               securities commission or regulatory authority and no proceedings
               for such purpose are pending or, to BioChem's knowledge,
               threatened;

        (j)    except as disclosed in the Registration Statement, or except for
               claims which have been provided for or reserved against in the
               most recent balance sheet of BioChem furnished to NAVA, or
               except as disclosed and accepted by the other party in the
               Agreement, there are no asserted claims or unasserted claims of
               which BioChem is aware or any litigation, action, suit or other
               claim by or before any court, tribunal, governmental agency or
               authority, securities commission or regulatory body that is
               material to the business, affairs, property or assets of
               BioChem;

        (k)    that the CPDL Agreements, the Technology Transfer Agreement and
               the Assignment and Amendment Agreement constitute valid and
               binding contracts enforceable according to their terms;


<PAGE>   20
                                      -20-

        (l)    that the Registration Statement with respect to the information
               provided by or pertaining to BioChem or the Institut
               Armand-Frappier, or to BioChem's knowledge, with respect to
               NAVA, does not contain an untrue statement of any material fact
               or omit any material fact required to be stated therein or
               necessary in order to make the statements therein not misleading
               in light of the circumstances under which they were made;

        (m)    the representations and warranties set out at Section 8 (a) of
               the Technology Transfer Agreement are true and correct;

        (n)    no consent, approval or other action of any third party is
               required to be obtained by BioChem, or to BioChem's knowledge,
               by NAVA in connection with the transactions contemplated in this
               Agreement except the consent of CPDL to the Assignment and
               Amendment Agreement and the requisite approvals of securities
               regulatory authorities and stock exchanges, each of which shall
               be obtained by BioChem prior to the Closing;

        (o)    the representations and warranties contained in this Section 4.2
               shall be true in all material respects on and as of the Closing
               Date with the same force and effect as though such
               representations and warranties had been made on and as of the
               Closing Date and shall survive any investigations by or on
               behalf of NAVA and shall survive the Closing.

                                  SECTION FIVE

                                    COVENANTS

5.1     Covenants: NAVA (for itself and for American Vaccine and AMVAX) on one
        part and BioChem, on the other part, each covenant and agree during the
        period commencing on the date hereof and continuing until the Closing
        Date, except as required in order to consummate the transactions
        contemplated hereby and except as required by law:

        (a)    to carry on their respective business in, and only in, the
               ordinary course in substantially the same manner as heretofore
               conducted and, to the


<PAGE>   21

                                      -21-

               extent consistent with such business to use all reasonable
               efforts to preserve intact their present business organizations
               and keep available the services of their present officers and
               employees and others having business dealings with them to the
               end that their respective goodwill and business shall be
               maintained;

        (b)    not to declare any dividends on or make other distributions in
               respect of their outstanding shares and not to amend their
               respective Articles or By-laws;

        (c)    not to issue, authorize or propose the issuance of, or purchase
               or propose the purchase of, any shares of their respective
               capital stock of any class or securities convertible into, or
               rights, warrants or options to acquire, any such shares or other
               convertible securities (other than such as are currently
               outstanding or contemplated by either corporation pursuant to
               written agreements, stock option plans, warrants, letters of
               intent, private placements or other commitments and which have
               been disclosed to the other party hereto in the Agreement);

        (d)    not to acquire, or agree to acquire, by amalgamating, merging or
               consolidating with, purchasing substantially all of the assets
               of or otherwise, any business or any corporation, partnership,
               association or other business organization or division thereof,
               which acquisition would be material to the business or financial
               condition of the affected corporation (except in the case of
               BioChem, the IAF Vaccines Transaction);

        (e)    not to sell, lease or otherwise dispose of any of their assets
               that are material, individually or in the aggregate, to their
               respective business or financial condition (except that American
               Vaccine may enter into a lease or purchase arrangement with
               respect to a manufacturing facility located in Beltsville,
               Maryland, upon terms and conditions subject to the approval of
               BioChem, such approval not to be unreasonably withheld);

        (f)    in the case of NAVA not to guarantee the payment of indebtedness
               or incur indebtedness for money borrowed except in the ordinary
               course of business or issue or sell any debt securities;


<PAGE>   22

                                      -22-

        (g)    to cooperate fully with each other in making available and
               providing access to all books, records, documents, management
               personnel and their independent auditors.

                                  SECTION SIX

                                    SURVIVAL

6.1     Survival of Representations, Warranties, Covenants and Undertakings:
        The representations, warranties, covenants and undertakings of BioChem
        and NAVA contained in this Agreement shall survive the Closing;
        provided, however, that except as otherwise provided in Section Seven,
        the representations and warranties contained in Section Four shall
        terminate on the second anniversary of the Closing Date. Except as
        otherwise provided herein, no claim shall be made for the breach of any
        representation or warranty contained in Section Four or under any
        certificate delivered with respect thereto under this Agreement after
        the date on which such representations and warranties terminate as set
        forth in this Section Six.

                                 SECTION SEVEN

                                INDEMNIFICATION

7.1     Indemnification by BioChem: BioChem agrees to indemnify and hold
        harmless NAVA, American Vaccine and AMVAX and their affiliates,
        successors and assigns from and against any and all (a) claims,
        demands, liabilities, losses, costs or damages (collectively, "Loss")
        and (b) reasonable attorneys', legal assistants' and accountants' fees
        and expenses (collectively, "Expense") incurred by NAVA, American
        Vaccine and AMVAX and their affiliates, successors and assigns in
        connection with or arising from (i) any breach by BioChem of any of its
        covenants in this Agreement or in any agreement or instrument
        contemplated hereby or thereby; (ii) any failure of BioChem to perform
        any of its obligations in this Agreement or any agreement or instrument
        contemplated hereby or thereby; or (iii) any breach of any
        representation of any warranty or the inaccuracy of any representation
        of BioChem contained or referred to in this Agreement or any
        certificate referred to


<PAGE>   23

                                      -23-

        herein delivered by or on behalf of BioChem pursuant hereto or thereto.
        The indemnification provided for in this Section 7.1 shall terminate
        two (2) years after the Closing Date (and no claims shall be made by
        NAVA, American Vaccine and AMVAX or their affiliates, successors or
        assigns under this Section 7.1 thereafter), except that the
        indemnification by BioChem shall continue as to (a) the covenant of
        BioChem set forth in Section 8.9, as to which no time limitation shall
        apply; (b) the representation and warranty set forth in Section 4.2(h),
        which shall expire no earlier than the date of expiration of the
        applicable period stipulated in the applicable statute of limitations
        with respect to liability for any such taxes, penalties, interest or
        liabilities; and (c) any Loss or Expense of which NAVA, American
        Vaccine and AMVAX or their affiliates, successors or assigns has
        notified BioChem in accordance with the requirements of Section 7.3 on
        or prior to the date such indemnification would otherwise terminate in
        accordance with this Section 7.1, as to which the obligation of BioChem
        shall continue until the liability of BioChem shall have been
        determined pursuant to this Section Seven, and BioChem shall have
        reimbursed NAVA, American Vaccine and AMVAX and their affiliates,
        successors or assigns for the full amount of such Loss and Expense in
        accordance with this Section Seven.

7.2     Indemnification by NAVA: NAVA agrees to indemnify and hold harmless
        BioChem and its affiliates, successors and assigns from and against any
        and all Loss and Expense incurred by BioChem and its affiliates,
        successors and assigns in connection with or arising from (a) any
        breach by NAVA of any of its covenants or agreements in this Agreement
        or any agreement or instrument contemplated hereby or thereby; (b) any
        failure by NAVA to perform any of its obligations under this Agreement
        or any agreement or instrument contemplated hereby or thereby; or (c)
        any breach of any warranty or the inaccuracy of any representation of
        NAVA contained or referred to in this Agreement or in any certificate
        referred to herein delivered by or on behalf of NAVA pursuant hereto or
        thereto. The indemnification provided for in this Section 7.2 shall
        terminate two (2) years after the Closing Date (and no claims shall be
        made by BioChem or its affiliates, successors or assigns under this
        Section 7.2 thereafter), except that the indemnification by NAVA shall
        continue as to i) the covenant of NAVA set forth


<PAGE>   24
                                      -24-

        in Section 8.9 as to which no time limitation shall apply; ii) the
        representation and warranty set forth in Section 4.1(m) which shall
        expire no earlier than the date of the expiration of the applicable
        period stipulated in the applicable statute of limitations with respect
        to liability for any such taxes, penalties, interest and liabilities;
        and iii) any Loss or Expense of which BioChem or its affiliates,
        successors or assigns has notified NAVA in accordance with the
        requirements of Section 7.3 on or prior to the date such
        indemnification would otherwise terminate in accordance with this
        Section 7.2, as to which the obligation of NAVA shall continue until
        the liability of NAVA shall have been determined pursuant to this
        Section Seven, and NAVA shall have reimbursed BioChem and its
        affiliates, successors and assigns for the full amount of such Loss and
        Expense in accordance with this Section Seven.

7.3     Notice of Claims: If NAVA or BioChem believes that any of the persons
        indemnified under this Section Seven has suffered or incurred any Loss
        or Expense, NAVA or BioChem shall so notify the other promptly in
        writing describing such Loss or Expense, the amount thereof, if known,
        and the method of computation of such Loss or Expense, all with
        reasonable particularity and containing a reference to the provisions
        of this Agreement or any other agreement or any certificate delivered
        pursuant hereto or thereto in respect of which such Loss or Expense
        shall have occurred. If any action at law or suit in equity is
        instituted by or against a third party with respect to which any of the
        indemnified persons intends to claim any liability or expense as Loss
        or Expense under this Section Seven, any such indemnified person shall
        promptly notify the indemnifying party of such action or suit.

7.4     Third Party Claim:

        (a)    Subject to paragraph (b) of this Section 7.4, the persons
               indemnified under this Section Seven shall have the right to
               conduct and control through counsel of their choosing, any third
               party claim, action or suit, and the persons indemnified may
               compromise or settle the same; provided that any of the
               indemnified persons shall give the indemnifying party advance
               notice of any proposed compromise or settlement and the
               indemnifying party shall have the right to


<PAGE>   25

                                      -25-

               approve or reject such proposed compromise or settlement. The
               indemnified person shall permit the indemnifying party to
               participate in the defense of any such action or suit through
               counsel chosen by it; provided that the fees and expenses of
               such counsel shall be borne by the indemnifying party. Subject
               to paragraph (b) of this Section 7.4, any compromise or
               settlement with respect to a claim for money damages effected
               after the indemnifying party by notice or settlement shall
               discharge the indemnifying party from liability with respect to
               the subject matter thereof, and no amount in respect thereof
               shall be claimed as Loss or Expense under this Section Seven.

        (b)    If the remedy sought in any action or suit referred to in
               paragraph (a) of this Section 7.4 is solely money damages and
               will have no continuing effect on the business of any
               indemnified person, the indemnifying party shall have 15
               business days after receipt of the notice referred to in the
               last sentence of Section 7.3 to notify the indemnified persons
               that it elects to conduct and control such action or suit. If
               the indemnifying party does not give the foregoing notice, the
               indemnified persons shall have the right to defend, contest,
               settle or compromise such action or suit in the exercise of
               their exclusive discretion, and the indemnifying party shall,
               upon request from any of the indemnified persons, promptly pay
               to such indemnified persons in accordance with the other terms
               of this Section Seven the amount of any Loss and all related
               Expenses resulting from such third-party claim.  If the
               indemnifying party gives the foregoing notice, the indemnifying
               party shall have the right to undertake, conduct and control,
               through counsel of its own choosing and at the sole expense of
               the indemnifying party, the conduct and settlement of such
               action or suit, and the indemnified persons shall cooperate with
               the indemnifying party in connection therewith; provided that
               (i) the indemnifying party shall not thereby permit to exist any
               lien, encumbrance or other adverse charge upon any asset of any
               indemnified person; (ii) the indemnifying party shall permit the
               indemnified persons to participate in such conduct or settlement
               through counsel chosen by


<PAGE>   26
                                      -26-

               the indemnified persons, but the fees and expenses of such
               counsel shall be borne by the indemnified persons except as
               provided in clause (iii) below; and (iii) the indemnifying party
               shall agree promptly to reimburse to the extent required under
               this Section Seven the indemnified persons for the full amount
               of any Loss resulting from such action or suit and all related
               Expenses incurred by the indemnified persons, except fees and
               expenses of counsel for the indemnified persons incurred after
               the assumption of the conduct and control of such action or suit
               by the indemnifying party. So long as the indemnifying party is
               contesting any such action or suit in good faith, the
               indemnified persons shall not pay or settle any such action or
               suit. Notwithstanding the foregoing, the indemnified persons
               shall have the right to pay or settle any such action or suit;
               provided that in such event the indemnified persons shall waive
               any right to indemnity therefore by the indemnifying party, and
               no amount in respect thereof shall be claimed as Loss or Expense
               under this Section Seven.

                                 SECTION EIGHT

                                 MISCELLANEOUS

8.1     Registration Rights: The parties agree that they shall have the
        respective registration rights in connection with the subsequent
        offering of the BioChem Common Shares and the Common Shares as set
        forth in Schedule 4 hereto which Schedule is made a part of this
        Agreement and is incorporated herein by reference.

8.2     NAVA not to vote its BioChem Common Shares: NAVA covenants and agrees
        with BioChem that, for so long as it holds BioChem Common Shares,
        neither it nor any other person shall exercise the voting rights
        conferred by any of the BioChem Common Shares, unless and until:

        i)     NAVA shall have sold or otherwise transferred any of the BioChem
               Common Shares to a person which is not a shareholder of NAVA and
               is not related to NAVA or to a NAVA shareholder, in which event,
               only those BioChem Common Shares that have been


<PAGE>   27
                                      -27-

               so sold or transferred shall confer voting rights;

        ii)    a secured creditor which is not a shareholder of NAVA and is not
               related to NAVA or to a NAVA shareholder shall, pursuant to a
               bona fide loan, guarantee or other instrument of indebtedness,
               have become the owner by foreclosure of any BioChem Common
               Shares, in which event, only those BioChem Common Shares in
               respect of which ownership was so acquired shall confer voting
               rights; or

        iii)   BioChem shall have issued and sold common shares from treasury
               to a person other than NAVA, a shareholder of NAVA or a person
               related to NAVA or to a NAVA shareholder pursuant to a private
               placement or public offering, including an issuance and sale to
               directors and officers of BioChem (excluding however, the
               issuance and sale of shares pursuant to employee or executive
               share purchase or stock option plans), but only to the extent of
               the number of BioChem Common Shares as is equal to the number of
               common shares so issued and sold by BioChem,

        provided that any sale, transfer or disposition in foreclosure pursuant
        to any agreement, plan or loan in existence as of the Closing Date
        shall not be taken into account for purposes of clauses (i), (ii) and
        (iii) of this Section 8.2.

8.3     Voting in favour of adoption of NAVA Share Option Plan: BioChem agrees
        to exercise the voting rights conferred by the Shares in favour of the
        adoption of the NAVA Share Option Plan to be adopted pursuant to the
        Agreement and Plan of Merger dated as of October 25, 1989, by and among
        NAVA, NAVA Merger Sub and American Vaccine.

8.4     Termination or Amendment: This Agreement may be terminated at any time
        prior to the filing and effectiveness of the Certificate of Merger with
        the Secretary of State of Delaware in accordance with the applicable
        provisions of the Delaware General Corporation Law (i) by mutual
        consent of the Boards of Directors of NAVA and BioChem, (ii) by either
        NAVA or BioChem if the share purchase has not been consummated by March
        31, 1990 (unless such party's breach caused the delay), or (iii) by
        either NAVA or BioChem if the


<PAGE>   28

                                      -28-

        other party is in breach of its obligations under this Agreement. In
        addition, this Agreement may be amended, modified or supplemented by
        mutual agreement in writing of the Boards of Directors of NAVA and
        BioChem at any time prior to the effective time referred to
        hereinabove.

        In the event that this Agreement shall be terminated pursuant to this
        Section 8.4, all further obligations of the parties hereto (other than
        Section 8.9) shall be terminated without further liability of either
        party to the other, provided that nothing herein shall relieve any
        party from its liability for its willful breach of this Agreement.

8.5     Notices: Any notice required or permitted to be given hereunder shall
        be given by facsimile transmission, by registered mail or by personal
        delivery (including delivery by courier) to the party for whom it is
        intended, addressed as follows:

<TABLE>
<S>                                         <C>
        TO NAVA:                            c/o American Vaccine
                                            1052 West Street, Laurel, MD 20707
                                            U.S.A.

                                            Fax #: 301-470-4219

        Attention:                          President

        with a copy to:                     American Vaccine
                                            1052 West Street, Laurel, MD 20707
                                            U.S.A.

                                            Fax #: 301-470-4219

        Attention:                          President

        with a copy to:                     Shaw, Pittman, Potts & Trowbridge
                                            2300 N Street, N.W.
                                            Washington, D.C.
                                            20037

                                            Fax #: 202-663-8007

        Attention:                          L. Duane Cheek
</TABLE>

<PAGE>   29
                                      -29-
<TABLE>
<S>                                         <C>
        TO BIOCHEM:                         IAF BioChem International Inc.
                                            10900 Hamon Street
                                            Montreal Quebec
                                            H3M 3A2

                                            Fax #: 514-335-9919

        Attention:                          President
</TABLE>

        Any notice, if delivered, shall be deemed to have been given or made on
        the date on which it was transmitted by facsimile or delivered in
        person or if mailed, shall be deemed to have been given on the third
        business day following the day on which it was mailed.

8.6     Further documents: The parties hereto undertake to do, sign, execute
        and deliver such other things, deeds of documents required to give full
        effect to the Agreement and the transactions contemplated hereby.

8.7     Binding effect: This Agreement may not be assigned by either party
        hereto without the prior written consent of the other party hereto and
        shall enure to the benefit of and be binding upon the parties hereto
        and their respective successors and permitted assigns.

8.8     Counterparts: This Agreement may be executed in counterparts, each of
        which shall be deemed an original, but all of which taken together
        shall constitute one and the same instrument.

8.9     Confidential Nature of Information: Each party agrees that it will
        treat in confidence all documents, materials and other information
        ("Confidential Information") which it shall have obtained regarding the
        other party (including all information regarding American Vaccine and
        AMVAX) during the course of the negotiations leading to the
        consummation of the transactions contemplated hereby and the
        preparation of this Agreement and other related documents, and, in


<PAGE>   30

                                      -30-

        the event the transactions contemplated hereby shall not be
        consummated, each party will return to the other party all copies of
        Confidential Information which have been furnished in connection
        therewith and neither party shall retain duplicates or copies of such
        Confidential Information nor use such Confidential Information for any
        business advantage. The obligation of each party to treat such
        documents, materials and other information in confidence shall not
        apply to any information which (i) such party can demonstrate was
        already lawfully in its possession prior to the disclosure thereof by
        the other party, (ii) is known to the public and did not become so
        known through any violation of a legal obligation, (iii) became known
        to the public through no fault of such party or (iv) is later lawfully
        acquired by such party from other sources.

8.10    Letter Agreement: The Agreement supersedes the letter agreement entered
        into between BioChem and American Vaccine dated as of July 28, 1989 as
        amended.

        IN WITNESS WHEREOF the parties hereto have duly executed this agreement
on the date first hereinabove mentioned.

                                           NORTH AMERICAN VACCINE INC.

                                           Per:/s/ Sharon Mates
                                              -----------------------------
                                               Name and Title
                                               Sharon Mates, Ph.D.
                                               President

                                           IAF BIOCHE NTERNATIONAL INC.

                                           Per:/s/
                                               ---------------------------
                                               Name and Title


<PAGE>   31


                                  INTERVENTION

               For good and valuable consideration, the receipt and sufficiency
of which is hereby acknowledged, American Vaccine and AMVAX, jointly and
severally with NAVA (American Vaccine and AMVAX hereby waiving the benefit of
division and discussion) hereby i) make all representations and warranties made
by NAVA in Section 4.1 of the Share Purchase Agreement entered into between
BioChem and NAVA dated January 17, 1990 (the "Share Purchase Agreement") (the
"NAVA Representations and Warranties"), only to the extent such representations
and warranties concern American Vaccine or AMVAX, provided that where the NAVA
Representations and Warranties are made to the knowledge of NAVA, the
representations and warranties made by American Vaccine or AMVAX as the case
may be, are made to their respective knowledge and ii) agree to be jointly and
severally bound with NAVA by the covenants, undertakings and obligations of
NAVA set out at Sections 3.2, 5.1, 6.1 and 7.2 of the Share Purchase Agreement.

               DATED this 17th day of January, 1990.

                                            AMERICAN VACCINE CORPORATION

                                     Per:/s/
                                         ---------------------------------
                                     Name and Title:  President

                                     Per:/s/
                                         ---------------------------------
                                     Name and Title Sr. V.P.


                                     AMVAX, INC.


                                     Per:/s/
                                         ---------------------------------
                                     Name and Title:  President

                                     Per:/s/
                                         ---------------------------------
                                     Name and Title:  President


<PAGE>   32
                                   Schedule 1
                        to the Share Purchase Agreement
                        entered into on January 17, 1990
                      between North American Vaccine, Inc.
                       and IAF BioChem International Inc.

<TABLE>
<CAPTION>
     Name of          Number         Exercise       Vesting    Expiry (1)    Payment to
     Holder         of shares         Price          Date         Date        Exercise
     -------        ---------        --------       -------    ----------    -----------
<S>                 <C>              <C>            <C>        <C>           <C>
Neil Flanzreich         5,000        $6.75             / /        / /         $33,750.00
Phillip Frost          30,000        $7.75            4/4/89    4/4/94       $232,500.00
Phillip Frost          30,000        $7.75            4/4/90    4/4/94       $232,500.00
Phillip Frost          40,000        $7.75            4/4/91    4/4/94       $310,000.00
Lance Gordon          107,546        $1.06           9/15/89    5/16/92      $113,998.76
Lance Gordon           25,000        $6.75           9/15/89    1/ /94       $168,750.00
Lance Gordon           25,000        $6.75           9/15/90    1/ /94       $168,750.00
Lance Gordon           25,000        $6.75           9/15/91    1/ /94       $168,750.00
Lance Gordon           25,000        $6.75           9/15/92    1/ /94       $168,750.00
Michael Healy          15,000        $7.25             / /       / /          $10,875.00
Lawrence Hineline       2,500        $7.25           5/17/90    5/17/94       $18,125.00
Lawrence Hineline       2,500        $7.25           5/17/91    5/17/94       $18,125.00
Lawrence Hineline       2,500        $7.25           5/17/92    5/17/94       $18,125.00
Lawrence Hineline       2,500        $7.25           5/17/93    5/17/94       $18,125.00
Carl Hochman           10,000        $2.00          11/13/86   11/13/91       $20,000.00
Lyle Kasprick          30,000        $7.75            4/4/89     4/4/94      $232,500.00
Lyle Kasprick          30,000        $7.75            4/4/90     4/4/94      $232,500.00
Lyle Kasprick          40,000        $7.75            4/4/91     4/4/94      $310,000.00
</TABLE>

- -------------------------

(1) If such Expiry Date for any NAVA Options is accelerated pursuant to the
terms of the applicable Option Agreement, the Expiry Date for the corresponding
BioChem Options shall be the later of the date 30 days following the accelerated
Expiry Date or the date 30 days following receipt by BioChem of written notice
pursuant to Section 2.2(c) of the Share Purchase Agreement.
<PAGE>   33
                                     - 2 -

<TABLE>
<S>                 <C>       <C>       <C>        <C>           <C>
Cormac Lannon       5,000     $7.25     (2)        2/14/94       $36,250.00

Cormac Lannon       5,000     $7.25     (3)        2/14/94       $36,250.00

[UNREADABLE] Maan   5,000     $7.25     __/__/__   __/__/__      $36,250.00
Lee

Wenlii Lin          5,500     $7.25      2/14/89    2/14/94      $39,875.00

Wenlii Lin          5,500     $7.25      2/14/90    2/14/94      $39,875.00

Wenlii Lin          5,500     $7.25      2/14/91    2/14/94      $39,875.00

Wenlii Lin          5,500     $7.25      2/14/92    2/14/94      $39,875.00

Wenlii Lin          5,500     $7.25      2/14/93    2/14/94      $39,875.00

George Marshall    15,000     $7.25     __/__/__   __/__/__     $108,750.00

Sharon Mates       30,000     $7.75       4/4/89     4/4/94     $232,500.00

Sharon Mates       30,000     $7.75       4/4/90     4/4/94     $232,500.00

Sharon Mates       40,000     $7.75       4/4/91     4/4/94     $310,000.00

Richard Pfenniger   5,000     $7.75       4/4/89     4/4/94      $38,750.00

Richard Pfenniger   5,000     $7.75       4/4/90     4/4/94      $38,750.00

Richard Pfenniger   5,000     $7.75       4/4/91     4/4/94      $38,750.00

Jacques Rubin      25,000     $7.25      5/17/90    5/17/94     $181,250.00

Jacques Rubin      25,000     $7.25      5/17/91    5/17/94     $181,250.00

Jacques Rubin      25,000     $7.25      5/17/92    5/17/94     $181,250.00

Jacques Rubin      25,000     $7.25      5/17/93    5/17/94     $181,250.00

Barbara Sampson     1,250     $7.75     10/21/89     4/4/94       $9,687.50

Barbara Sampson     1,250     $7.75       3/5/90     4/4/94       $9,687.50
</TABLE>

- -----------
(2) The date of completion of American Vaccine's Beltsville plant.

(3) The date on which American Vaccine's Beltsville plant commences operation.
<PAGE>   34
                                     - 3 -

<TABLE>
<S>                 <C>       <C>       <C>            <C>       <C>
Barbara Sampson      1,250    $7.75      7/3/90 (4)    4/4/94    $  9,687.50

Barbara Sampson      1,250    $7.75     10/31/90(4)    4/4/94    $  9,687.50

Barbara Sampson      1,250    $7.75      2/28/91(4)    4/4/94    $  9,687.50

Barbara Sampson      1,250    $7.75      6/28/91(4)    4/4/94    $  9,687.50

Barbara Sampson      1,250    $7.75     10/26/91(4)    4/4/94    $  9,687.50

Barbara Sampson      1,250    $7.75      2/23/92(4)    4/4/94    $  9,687.50

Ronald Sekura       54,565    $0.004     9/15/89       5/16/92   $    618.26

Ronald Sekura       25,000    $6.75      9/15/89       1/__/94   $168,750.00

Ronald Sekura       25,000    $6.75      9/15/90       1/__/94   $168,750.00

Ronald Sekura       25,000    $6.75      9/15/91       1/__/94   $168,750.00

Ronald Sekura       25,000    $6.75      9/15/92       1/__/94   $168,750.00

Ronald Sekura       12,500    $6.75     __/__/__       __/__/__  $ 84,375.00

Ronald Sekura       12,500    $6.75     __/__/__       __/__/__  $ 84,375.00

Victor Siegel        3,500    $2.75      8/22/86        8/22/91  $  9,625.00

Jeffrey Spragens    30,000    $8.25      4/4/89         4/4/94   $247,500.00

Jeffrey Spragens    30,000    $8.25      4/4/90         4/4/94   $247,500.00

Jeffrey Spragens    40,000    $8.25      4/4/91         4/4/94   $330,000.00

Yan-Ling Zhang       5,000    $7.75      4/4/89         4/4/94   $ 38,750.00

Yan-Ling Zhang       5,000    $7.75      4/4/90         4/4/94   $ 38,750.00

Yan-Ling Zhang       5,000    $7.75      4/4/91         4/4/94   $ 38,750.00
</TABLE>

WARRANTS

<TABLE>
<S>                <C>         <C>         <C>        <C>         <C>
   Name of         Number of   Exercise    Vesting    Expiry      Payment to
Warrant Holder      Shares      Price        Date      Date        Exercise
- --------------     ---------   --------    -------    ------      ----------
B.N. Wolf & Co.      64,688      $4.80     7/31/86    7/31/90     $310,502.40
</TABLE>

- --------------
(4)  Vesting is also conditioned upon the exercise by the National Institute of
     health of its option to review its contract with American Vaccine for the
     provision of bulk pertussis toxoid for each such 120-day period.

<PAGE>   35


                                   SCHEDULE 2

                            SHAREHOLDERS' AGREEMENT
                (See Exhibit 9.1 to the Registration Statement)


<PAGE>   36


                                   SCHEDULE 3

                         TECHNOLOGY TRANSFER AGREEMENT
                 See Exhibit 2.4 to the Registration Statement)


<PAGE>   37


                                   SCHEDULE 4

                              REGISTRATION RIGHTS

                                  SECTION ONE
                          BIOCHEM REGISTRATION RIGHTS

        1.1. Certain Definitions. As used in this Section 1 to Schedule 4 of
the Share Purchase Agreement entered into between North American Vaccine, Inc.
and IAF BioChem International Inc. on January 17, 1990, (the "Share Purchase
Agreement") the following terms shall have the following respective meanings,
and all other defined terms shall have the meanings ascribed thereto in the
Share Purchase Agreement.

        "Registrable Securities" shall mean (i) the Common Shares and (ii) any
NAVA common shares issued pursuant to the Options or issued or issuable in
respect of the Common Shares, upon any stock split, stock dividend,
recapitalization, or similar event, so long as the Common Shares and any NAVA
common shares issued in respect of the Common Shares are owned by BioChem.

        The terms "register," "registered" and "registration" refer to a
registration effected by preparing and filing a registration statement in
compliance with the Securities Act, and the declaration or ordering of the
effectiveness of such registration statement.

        "Registration Expenses" shall mean all expenses incurred by NAVA in
complying with Sections 1.2 and 1.3 hereof, including, without limitation, all
registration, qualification and filing fees, printing expenses, escrow fees,
fees and disbursements of counsel for NAVA, blue sky fees


<PAGE>   38


                                      -2-


and expenses (including those of counsel for the underwriters(s)), marketing
expenses and the expense of any special audits incident to or required by any
such registration (but excluding the compensation of regular employees of NAVA
which shall be paid by NAVA).

        "SEC" shall mean the Securities and Exchange Commission or any other
Federal agency at the time administering the Securities Act.

        "Selling Expenses" shall mean all underwriting discounts, selling
commissions and stock transfer taxes applicable to the securities registered by
BioChem and all fees and disbursements of counsel for BioChem.

        "Securities Act" shall mean the Securities Act of 1933.

        1.2. Requested Registration. (a) Request for Registration. BioChem
shall have a one time right pursuant to this Section 1.2 to request NAVA to
register the offering of up to all but not less than 25% of BioChem's
Registrable Securities owned by BioChem as of the Closing Date. In case NAVA
shall receive from BioChem a written request pursuant to Section 1.2(b) hereof
that NAVA effect any registration, qualification or compliance with respect to
the Registrable Securities, NAVA will, as soon as practicable, use its best
efforts to effect such registration, qualification or compliance (including,
without limitation, the execution of an undertaking to file post-effective
amendments, appropriate qualification under applicable blue sky or other state
securities laws and appropriate compliance with applicable regulations issued
under the Securities Act and any other governmental


<PAGE>   39

                                      -3-

requirements or regulations) as may be so requested and as would permit or
facilitate the sale and distribution of all Registrable Securities owned by
BioChem; provided, however, that NAVA shall not be obligated to take any action
to effect any such registration, qualification or compliance pursuant to this
Section 1.2:

        (i) in any particular jurisdiction in which NAVA would be required to
execute a general consent to service of process in effecting such registration,
qualification or compliance unless NAVA is already subject to service in such
jurisdiction and except as may be required by the Securities Act;

        (ii) prior to the first anniversary of the Closing Date;

        (iii) during the period starting with the date 50 days prior to NAVA's
estimated date of filing of, and ending on the date 90 days immediately
following the effective date of any registration statement pertaining to
securities of NAVA (other than a registration of securities in a Rule 145
transaction or with respect to an employee benefit plan); provided that NAVA is
actively employing in good faith all reasonable efforts to cause such
registration statement to become effective and that NAVA's estimate of the date
of filing of such registration statement is made in good faith;

        (iv) after NAVA has effected one such registration pursuant to this
subparagraph 1.2(a) and such registration has been declared or ordered
effective;


<PAGE>   40

                                      -4-

        (v) if NAVA shall furnish to BioChem a certificate signed by the
President of NAVA stating that in the good fath judgment of the Board of
Directors it would be seriously detrimental to NAVA or its shareholders for a
registration statement to be filed in the near future, in which case NAVA's
obligation to use its best efforts to register, qualify or comply under this
Section 1.2 shall be deferred not more than once for a period not to exceed 90
days; or

        (vi) after the fifth anniversary of the Closing Date;

Subject to the foregoing clauses (i) through (vi), NAVA shall file a
registration statement covering an offering of the Registrable Securities so
requested to be registered as soon as practicable after receipt of the request
of BioChem.

        (b) Notice. The right of BioChem to registration pursuant to Section
1.2 shall be conditioned upon NAVA's receipt of written notice from BioChem
which shall include a description of BioChem's proposed plan of distribution of
its Registrable Securities and the underwriting arrangements, if any. In the
context of such registration with a view to a non-exempt offering, NAVA shall
have the right to approve such plan of distribution and underwriting
arraigements, which approval will not be unreasonably withheld. Nothing herein
shall apply to an offering by way of private placement.

        1.3. Piggyback Registration Rights.

        (a) Notice of Registration.  If, at any time or from time to time, NAVA
shall determine to register any of its


<PAGE>   41

                                      -5-

securities, either for its own account or the account of a securityholder or
holders (other than BioChem) exercising their respective demand registration
rights, other than (i) a registration relating solely to employee benefit
plans, or (ii) a registration relating solely to a SEC Rule 145 transaction,
NAVA will:

        (A) promptly give to BioChem written notice thereof; and

        (B) include in such registration (and any related qualification under
blue sky laws or other compliance), and in any underwriting involved therein,
all the Registrable Securities specified in a written request or requests, made
within 30 days after receipt of such written notice from NAVA by BioChem;
provided, however, that NAVA shall have no obligation to include in such
registration a number of Registrable Securities equal to less than 25% of the
Registrable Securities owned by BioChem as of the Closing Date.

        (b) Underwriting. If the registration of which NAVA gives notice is for
a registered public offering involving an underwriting, NAVA shall so advise
BioChem as a part of the written notice given pursuant to Section 1.3(a) above.
In such event, the right of BioChem to registration pursuant to Section 1.3(a)
shall be conditioned upon BioChem's participation in such underwriting and the
inclusion of Registrable Securities in the underwriting to the extent provided
herein. BioChem, if it is proposing to distribute its Registrable Securities
through such underwriting, shall (together with NAVA) enter into an
underwriting agreement in customary form with the managing underwriter selected
for


<PAGE>   42
                                      -6-

such underwriting by NAVA. Notwithstanding any other provision of this Section
1.3, if the managing underwriter determines that marketing factors require a
limitation of the number of Registrable Securities to be underwritten, the
managing underwriter may limit the Registrable Securities to be included in
such registration or completely exclude the Registrable Securities from such
registration. NAVA shall so advise BioChem of the number of Registrable
Securities that may be included in the registration and underwriting. If
BioChem disapproves of the terms of any such underwriting, it may elect to
withdraw therefrom, without the loss to BioChem of any rights under this
Section 1, by written notice to NAVA and the managing underwriter. Any
securities excluded or withdrawn from such underwriting shall be withdrawn from
such registration, and shall not be transferred in a public distribution prior
to 90 days after the effective date of the registration statement relating
thereto. NAVA may include common shares held by shareholders other than BioChem
in a registration statement pursuant to Section 1.2 and this Section 1.3 only
if, and to the extent, the amount of Registrable Securities includable in such
registration would not thereby be diminished.

        (c) Right to Terminate Registration. NAVA shall have the right to
terminate or withdraw any registration initiated by it under this Section 1.3
prior to the effectiveness of such registration whether or not BioChem has
elected to include securities in such registration.

        (d) Termination of Registration Rights. BioChem's registration rights
under this Section 1.3 shall terminate on the fifth anniversary of the Closing
Date.


<PAGE>   43

                                      -7-

        1.4. Expenses of Registration. All Registration Expenses and Selling
Expenses incurred in connection with a registration pursuant to Section 1.2
shall be borne by BioChem; provided, however, that in the event one or more
holders of NAVA common shares exercise any piggyback registration rights with
respect to a registration under Section 1.2, BioChem shall have no obligation
to pay for that portion of the Registration Expenses incurred as a result of
such holder's or holders' exercise of such piggyback registration rights. All
Selling Expenses incurred in connection with any registration pursuant to
Section 1.3 shall be borne by BioChem and a pro rata share of the Registration
Expenses incurred in connection with any registration pursuant to Section 1.3
shall be borne by BioChem on the basis of the number of Registrable Securities
so registered divided by the aggregate number of shares registered pursuant to
such registration.

        1.5. Registration Procedures. In the case of each registration,
qualification or compliance effected by NAVA pursuant to this Section 1, NAVA
will keep BioChem advised in writing as to the initiation of each registration,
qualification and compliance and as to the completion thereof. At the expense
of BioChem and/or NAVA as determined pursuant to Section 1.4, NAVA will:

        (a) prepare and file with the SEC a registration statement with respect
to such securities and use its best efforts to cause such registration
statement to become and remain effective for at least 120 days, and prepare and
file with the SEC such amendments to such registration statement and
supplements to the prospectus contained therein as may be necessary to keep
such registration statement effective


<PAGE>   44

                                      -8-

or current, as the case may be, for at least 120 days; provided that no such
registration shall constitute a shelf registration under Rule 415 promulgated
by the SEC under the Securities Act;

        (b) enter into a written underwriting agreement in customary form and
substance reasonably satisfactory to NAVA, BioChem and the managing underwriter
or underwriters of the public offering of such securities, if the offering is
to be underwritten in whole or in part;

        (c) furnish to BioChem if it is participating in such registration and
to the underwriters of the securities being registered such reasonable number
of copies of the registration statement, preliminary prospectus, final
prospectus and such other documents as such underwriters may reasonably request
in order to facilitate the public offering of such securities;

        (d) use its best efforts to register or qualify the securities covered
by such registration statement under such state securities or blue sky laws of
such jurisdictions as BioChem may reasonably request within ten days prior to
the original filing of such registration statement, except that NAVA shall not
for any purpose be required to execute a general consent to service of process
or to qualify to do business as a foreign corporation in any jurisdiction where
it is not so qualified;

        (e) notify BioChem, promptly after it shall receive notice thereof, of
the time when such registration statement has become effective or a supplement
to any prospectus forming a part of such registration statement has been filed;


<PAGE>   45

                                      -9-

        (f) notify BioChem promptly of any request by the SEC for the amending
or supplementing of such registration statement or prospectus or for additional
information;

        (g) prepare and file with the SEC promptly upon the request of BioChem,
any amendments or supplements to such registration statement or prospectus
which, in the reasonable opinion of counsel for BioChem, is required under the
Securities Act or the rules and regulations thereunder in connection with the
distribution of the Registrable Securities by BioChem;

        (h) prepare and promptly file with the SEC, and promptly notify BioChem
of the filing of, such amendment or supplement to such registration statement
or prospectus as may be necessary to correct any statements or omissions if, at
the time when a prospectus relating to such securities is required to be
delivered under the Securities Act, any event has occurred as the result of
which any such registration statement or prospectus contains an untrue
statement of a material fact or omits to state any material fact necessary to
make the statements therein, not misleading, in the light of the circumstances
in which they were made;

        (i) in case BioChem or any underwriter for BioChem is required to
deliver a prospectus at a time when the prospectus then in effect may no longer
be used under the Securities Act, prepare promptly upon request such amendment
or amendments to such registration statement and such prospectuses as may be
necessary to permit compliance with the requirements of the Securities Act;


<PAGE>   46

                                      -10-

        (j) advise BioChem, promptly after it shall receive notice or obtain
knowledge thereof, of the issuance of any stop order by the SEC suspending the
effectiveness of such registration statement or the initiation or threatening
of any proceeding for that purpose and promptly use its best efforts to prevent
the issuance of any stop order or to obtain its withdrawal if such stop order
should be issued; and

        (k) at the request of BioChem, furnish on the effective date of the
registration statement and, if such registration includes an underwritten
public offering, at the closing provided for in the underwriting agreement, (i)
an opinion, dated each such date, of the counsel representing NAVA for the
purposes of such registration, addressed to the underwriters, if any, and to
BioChem, covering such matters with respect to the registration statement, the
prospectus and each amendment or supplement thereto, proceedings under state
and Federal securities laws, other matters relating to NAVA, the securities
being registered and the offer and sale of such securities as are customarily
the subject of opinions of issuer's counsel provided to underwriters in
underwritten public offerings, and (ii) to the extent NAVA's accounting firm is
willing to do so, a letter dated each such date, from the independent certified
public accountants of NAVA, addressed to the underwriters, if any, and to
BioChem, stating that they are independent certified public accountants of
NAVA, addressed to the underwriters, if any, and to BioChem, stating that they
are independent certified public accountants within the meaning of the
Securities Act and that in the opinion of such accountants the financial
statements and other financial data of NAVA included in the registration
statement or the prospectus or any amendment or supplement thereto comply in
all material respects with the applicable accounting


<PAGE>   47


                                      -11-


requirements of the Securities Act, and additionally covering such other
financial matters, including information as to the period ending not more than
five business days prior to the date of such letter with respect to the
registration statement and prospectus, as the underwriters or BioChem may
reasonably request.

        1.6. Indemnification. (a) NAVA will indemnify BioChem, each of its
officers, directors and partners, and each person controlling BioChem within
the meaning of Section 15 of the Securities Act, with respect to which
registration, qualification or compliance has been effected pursuant to this
Section 1, and each underwriter, if any, and each person who controls any
underwriter within the meaning of Section 15 of the Securities Act, against all
expenses, claims, losses, damages or liabilities (or actions in respect
thereof), including any of the foregoing incurred in settlement of any
litigation, commenced or threatened, arising out of or based on any untrue
statement (or alleged untrue statement) of a material fact contained in any
registration statement, prospectus, offering circular or other document, or any
amendment or supplement thereto, incident to any such registration,
qualification or compliance, or based on any omission (or alleged omission) to
state therein a material fact required to be stated therein or necessary to
make the statements therein, in light of the circumstances in which they were
made, not misleading, or any violation by NAVA of any rule or regulation
promulgated under the Securities Act applicable to NAVA in connection with any
such registration, qualification or compliance, and NAVA will reimburse
BioChem, each of its officers, directors and partners, and each person
controlling BioChem, each such underwriter and


<PAGE>   48

                                      -12-

each person who controls any such underwriter, for any legal and any other
expenses reasonably incurred in connection with investigating, preparing or
defending any such claim, loss, damage, liability or action, provided that NAVA
will no. be liable in any such case to the extent that any such claim, loss,
damage, liability or expense arises out of or is based on any untrue statement
or omission or alleged untrue statement or omission, made in reliance upon and
in conformity with written information furnished to NAVA by an instrument duly
executed by BioChem or any such controlling person or underwriter expressly for
use therein.

        (b) BioChem will indemnify NAVA, each of its directors and officers,
each underwriter, if any, of NAVA's securities covered by such a registration
statement and each person who controls NAVA or such underwriter within the
meaning of Section 15 of the Securities Act, against all expenses, claims,
losses, damages or liabilities (or actions in respect thereof), including any
of the foregoing incurred in settlement of any litigation, commenced or
threatened, arising out of or based on any untrue statement (or alleged untrue
statement) of a material fact contained in any such registration statement,
prospectus, offering circular or other document, or any amendment or supplement
thereto, incident to any such registration, qualification or compliance, or
based on any omission (or alleged omission) to state therein a material fact
required to be stated therein or necessary to make the statements therein, in
light of the circumstances in which they were made, not misleading, and will
reimburse NAVA, each such underwriter and each person who controls any such
underwriter, for any legal and any other expenses reasonably incurred in
connection with investigating, preparing or defending any


<PAGE>   49
                                      -13-

such claim, loss, damage, liability or action, in each case to the extent, but
only to the extent, that such untrue statement (or alleged untrue statement) or
omission (or alleged omission) is made in such registration statement,
prospectus, offering circular or other document in reliance upon and in
conformity with written information furnished to NAVA by an instrument duly
executed by BioChem expressly for use therein.

        (c) Each party entitled to indemnification under this Section 1.6 (the
"Indemnified Party") shall give notice to the party required to provide
indemnification (the "Indemnifying Party") promptly after such Indemnified
Party has actual knowledge of any claim as to which indemnity may be sought,
and shall permit the Indemnifying Party to assume the defense of any such claim
or any litigation resulting therefrom, provided that counsel for the
Indemnifying Party, who shall conduct the defense of such claim or litigation,
shall be approved by the Indemnified Party (whose approval shall not
unreasonably be withheld), and the Indemnified Party may participate in such
defense at such party's expense, and provided further that the failure of any
Indemnified Party to give notice as provided herein shall not relieve the
Indemnifying Party of its obligations under this Section 1 unless the failure
to give such notice is materially prejudicial to an Indemnifying Party's
ability to defend such action. No Indemnifying Party, in the defense of any
such claim or litigation, shall, except with the consent of each Indemnified
Party, consent to entry of any judgement or enter into any settlement which
does not include as an unconditional term thereof the giving by the claimant or
plaintiff to such Indemnified Party of a release from all liability in respect
to such claim or litigation.


<PAGE>   50

                                      -14-

        1.7. Information by BioChem. It shall be a condition precedent to the
obligations of NAVA to effect a registration pursuant to this Section 1 that
BioChem shall furnish to NAVA such information regarding BioChem, the
Registrable Securities held by it and the distribution proposed by BioChem as
NAVA may request in writing and as shall be required in connection with any
registration qualification or compliance referred to in this Section 1.

        1.8. No Transfer of Registration Rights. The rights to cause NAVA to
register securities granted to BioChem under Section 1.2 and 1.3 are not
assignable in connection with any transfer or assignment of Registrable
Securities by BioChem or otherwise.

        1.9. Limitation on Injunctions. BioChem shall not have any right to
obtain or seek an injunction restraining or otherwise delaying any registration
as the result of any controversy that might arise with respect to the
interpretation or implementation of the provisions of this Section 1.

                                  SECTION TWO
                            NAVA REGISTRATION RIGHTS

        2.1. Certain Definitions. As used in this Section 2 to Schedule 4 of
the Share Purchase Agreement, the following terms shall have the following
respective meanings, and all other defined terms shall have the meaning
ascribed thereto in the Share Purchase Agreement.


<PAGE>   51

                                      -15-

        "Commissions" shall mean the securities commissions of the Provinces of
Quebec and Ontario.

        "Securities" shall mean (i) the BioChem Common Shares and (ii) any
BioChem common shares issued or issuable in respect of the BioChem Common
Shares, upon any stock split, stock dividend, recapitalization, or similar
event, so long as the BioChem Common Shares and any BioChem Common Shares
issued in respect of the BioChem Common Shares are owned by NAVA.

        The terms "qualify," and "qualified for distribution" refer to
qualification for distribution (including, where appropriate, distribution to
the public) of Securities effected by preparing and filing with the Commissions
a prospectus in compliance with the Securities Act.

        "Expenses" shall mean all expenses incurred by BioChem in complying
with Sections 2.2 and 2.3 hereof, including, without limitation, all
qualification and filing fees, printing expenses, escrow fees, fees and
disbursements of counsel for BioChem (including those of counsel for the
underwriters(s)), marketing expenses and the expense of any special audits
incident to or required by any such qualification for distribution (but
excluding the compensation of regular employees of BioChem which shall be paid
by BioChem).

        "Selling Expenses" shall mean all underwriting discounts, selling
commissions and share transfer taxes applicable to the securities qualified for
distribution by NAVA and all fees and disbursements of counsel for NAVA.


<PAGE>   52
                                      -16-

        "Securities Acts" shall mean the securities acts of the Provinces of
Quebec and Ontario.

        2.2. Requested Qualification For Distribution. (a) Request for
Qualification for Distribution. NAVA shall have a one time right pursuant to
this Section 2.2 to request BioChem to qualify for distribution the offering of
all, but not a portion of the Securities owned by NAVA at the time of such
request. In case BioChem shall receive from NAVA a written request that BioChem
effect any qualification for distribution with respect to the Securities,
BioChem will, as soon as practicable, use its best efforts to effect such
qualification for distribution (including, without limitation, appropriate
compliance with the Securities Acts and any other securities regulatory and
stock exchange requirements or regulations) as may be so requested and as would
permit or facilitate the sale and distribution of all Securities owned by NAVA;
provided, however, that BioChem shall not be obligated to take any action to
effect any such qualification for distribution pursuant to this Section 2.2:

        (i) in any particular jurisdiction in which BioChem would be required
to execute a general consent to service of process in effecting such
qualification for distribution unless BioChem is already subject to service in
such jurisdiction and except as may be required by the Securities Act;

        (ii) prior to the first anniversary of the Closing Date;


<PAGE>   53

                                      -17-

        (iii) during the period starting with the date 60 days prior to
BioChem's estimated date of filing of, and ending on the date 90 days
immediately following the date of any preliminary prospectus qualifying the
distribution of securities of BioChem (other than a distribution of securities
under Section 50 of the Securities Act (Quebec) or Sections 71(1)(h) or
71(1)(i) of the Securities Act (Ontario) or with respect to any employee
benefit plan); provided that BioChem is actively employing in good faith all
reasonable efforts to file its final prospectus and obtain receipts in respect
thereof from the Commissions and that BioChem's estimate of the date or filing
of the preliminary prospectus is made in good faith;

        (iv) after BioChem has effected one such qualification pursuant to this
subparagraph 2.2(a), and receipts in respect of a final prospectus have been
issued under the Securities Acts in connection therewith and the securities
offered pursuant to such qualification for distribution have been sold;

        (v) if BioChem shall furnish to NAVA a certificate signed by the
President of BioChem stating that in the good faith judgment of the Board of
Directors it would be seriously detrimental to BioChem or its shareholders for
a prospectus to be filed in the near future, in which case BioChem's obligation
to use its best efforts to qualify under this Section 2.2 shall be deferred,
not more than once in any 12-month period, for a period not to exceed 90 days;
or

        (vi) after the fifth anniversary of the Closing Date.


<PAGE>   54
                                      -18-

        Subject to the foregoing clauses (i) through (vi), BioChem shall file a
prospectus qualifying a distribution of Securities so requested to be qualified
for distribution as soon as practicable, after receipt of the request of NAVA.

        (b) Notice. The right of NAVA to qualification for distribution
pursuant to Section 2.2 shall be conditioned upon BioChem's receipt of written
notice from NAVA which shall include a description of NAVA's proposed plan of
distribution and its Securities and the underwriting arrangements, if any.

        (c) Offering of Securities in the United States. If at the time of any
offering pursuant to Section 2.2, the common shares of BioChem are registered
under the Securities Act of 1933 and in connection with such offering, NAVA
desires to offer for sale its Securities in the United States, the parties
hereto shall negotiate in good faith, terms and conditions for the registration
of such securities in the United States comparable to those set forth in
Section 1.2 hereof.

        2.3. Piggyback Rights.

        (a) Notice of Qualification for Distribution. If, at any time or from
time to time, BioChem shall determine to qualify for distribution to the public
by prospectus any of its common shares, either for its own account or the
account of a securityholder or holders (other than NAVA) exercising their
respective demand qualification for distribution rights, other than (i) a
distribution relating solely to employee benefit plans, or (ii) a distribution
that is


<PAGE>   55

                                      -19-

exempted from the prospectus requirements of the Securities Acts, BioChem will:

        (A) promptly give to NAVA written notice thereof; and

        (B) include in such qualification for distribution and in any
underwriting involved therein, all the Securities specified in a written
request or requests, made within 30 days after receipt of such written notice
from BioChem by NAVA; provided, however, that BioChem shall have no obligation
to include in such qualification for distribution a number of Securities equal
to less than 25% of the Securities owned by NAVA as of the Closing Date.

        (b) Underwriting. If the qualification for distribution of which
BioChem gives notice is for a public offering involving an underwriting,
BioChem shall so advise NAVA as a part of the written notice given pursuant to
Section 2.3(a) above. In such event, the rights of NAVA pursuant to Section
2.3(a) shall be conditioned upon NAVA's participation in such underwriting and
the inclusion of Securities in the underwriting to the extent provided herein.
NAVA, if it is proposing to distribute its Securities through such
underwriting, shall (together with BioChem) enter into an underwriting
agreement in customary form with the managing underwriter selected for such
underwriting by BioChem. Notwithstanding any other provision of this Section
2.3, if the managing underwriter determines that marketing factors require a
limitation of the number of Securities to be underwritten, the managing
underwriter may limit the Securities to be included in such distribution or
completely exclude the Securities from such distribution. BioChem shall so
advise NAVA of the number of


<PAGE>   56

                                      -20-

Securities that may be included in the distribution and underwriting. If NAVA
disapproves of the terms of any such underwriting, it may elect to withdraw
therefrom, without the loss to NAVA of any rights under this Section 2, by
written notice to BioChem and the managing underwriter. Any securities excluded
or withdrawn from such underwriting shall not be transferred in a public
offering prior to 90 days after the date of the final prospectus relating
thereto. BioChem may include common shares held by shareholders other than NAVA
in a distribution pursuant to Section 2.2 and this Section 2.3 only if, and to
the extent, the amount of Securities includable in such distribution would not
thereby be diminished.

        (c) Right to Terminate Distribution BioChem shall have the right to
terminate or withdraw from any distribution initiated by it under this Section
2.3 prior to the date of closing of such distribution whether or not NAVA has
elected to include Securities in such distribution.

        (d) Termination of Registration Rights.  NAVA's registration rights
under this Section 2.3 shall terminate on the fifth anniversary of the Closing
Date.

        2.4. Expenses All Expenses and Selling Expenses incurred in connection
with a distribution pursuant to Section 2.2 shall be borne by NAVA; provided,
however, that in the event one or more holders of BioChem common shares
exercise any piggyback rights with respect to a qualification for distribution
under Section 2.2, NAVA shall have no obligation to pay for that portion of the
Expenses incurred as a result of such holder's or holders' exercise of such
piggyback rights. All Selling Expenses incurred in


<PAGE>   57

                                      -21-

connection with any distribution pursuant to Section 2.3 shall be borne by NAVA
and a pro rata share of the Expenses incurred in connection with any
distribution pursuant to Section 2.3 shall be borne by NAVA on the basis of the
number of Securities so qualified for a distribution divided by the aggregate
number of shares qualified for distribution pursuant to such qualification for
distribution.

        2.5. Qualification of Distribution Procedures. In the case of a
distribution effected by BioChem pursuant to this Section 2., BioChem will keep
NAVA advised in writing as to the initiation of each such distribution and as
to the completion thereof. At the expense of NAVA and/or BioChem as determined
pursuant to Section 2.4, BioChem will:

        (a) prepare and file with the Commissions a preliminary prospectus with
respect to such securities and use its best efforts to prepare and file with
the Commissions a final prospectus; provided that no such prospectus shall
constitute a shelf prospectus under Section 24.1 of the Securities Act (Quebec)
or Section 52.2 of the Securities Act (Ontario).

        (b) enter into a written underwriting agreement in customary form and
substance reasonably satisfactory to BioChem, NAVA and the managing underwriter
or underwriters of the public offering of such securities, if the distribution
is to be underwritten in whole or in part;

        (c) furnish to NAVA if it is participating in such distribution and to
the underwriters of the securities being qualified such reasonable number of
copies of the preliminary prospectus, final prospectus and such other


<PAGE>   58

                                      -22-

documents as such underwriters may reasonably request in order to facilitate
the public offering of such securities;

        (e) notify NAVA, promptly after it shall receive notice thereof, of the
time when receipts in respect of the preliminary and final prospectuses have
been issued by the Commissions.

        (f) notify NAVA promptly of any request by the Commissions for the
amending or supplementing of the preliminary and final prospectuses or for
additional information;

        (g) prepare and file with the Commissions promptly upon the request of
NAVA, any amendments or supplements to the preliminary or final prospectuses
which, in the reasonable opinion of counsel for NAVA, is required under the
Securities Act in connection with the distribution of the Securities by NAVA;

        (h) prepare and promptly file with the Commissions, and promptly notify
NAVA of the filing of, such amendment or supplement to the preliminary or final
prospectuses if, since the filing of the preliminary or final prospectus, a
change in a "material fact" (as such expression is defined under the Securities
Acts) has occurred which is or may be of such a nature as to render such
prospectus untrue or misleading or result in a misrepresentation (as defined in
the Securities Acts) therein likely to affect the value or the market price of
the securities to be distributed or which would result in such prospectus not
complying (to the extent such compliance is required) with the Securities Acts.


<PAGE>   59

                                      -23-

        (i) in case NAVA or any underwriter for NAVA is required to deliver a
prospectus at a time when the prospectus then in effect may no longer be used
under the Securities Acts, prepare promptly upon request such amendment or
amendments to such prospectuses as may be necessary to permit compliance with
the requirements of the Securities Acts;

        (j) advise NAVA, promptly after it shall receive notice or obtain
knowledge thereof, of the issuance of any cease trade order by the Commissions
relating to the distribution of the securities or the initiation or threatening
of any proceeding for that purpose and promptly use its best efforts to prevent
the issuance of any cease trade order or to obtain its withdrawal if such cease
trade order should be issued; and

        (k) at the request of NAVA, furnish on the closing date provided for in
the underwriting agreement, (i) an opinion, dated such date, of the counsel
representing BioChem for the purposes of such qualification for distribution,
addressed to the underwriters, if any, and to NAVA, covering such matters with
respect to the prospectus and each amendment or supplement thereto, proceedings
under applicable securities laws, other matters relating to BioChem, the
securities being qualified for distribution and the offer and sale of such
securities as are customarily the subject of opinions of issuer's counsel
provided to underwriters in underwritten public offerings, and (ii) to the
extent BioChem's accounting firm is willing to do so, a letter dated such date,
from the independent auditors of BioChem, addressed to the underwriters, if
any, and to NAVA,


<PAGE>   60
                                      -24-


stating that they are independent auditors and that in the opinion of such
auditors, the financial statements and other financial data of BioChem included
in the prospectus or any amendment or supplement thereto comply in all material
respect with the applicable accounting requirements of the Securities Acts, and
additionally covering such other financial matters, including information as to
the period ending not more than five business days prior to the date of such
letter with respect to the prospectus, as the underwriters or NAVA may
reasonably request.

        2.6. Indemnification. (a) BioChem will indemnify NAVA, each of its
officers and directors and each person controlling NAVA within the meaning of
the Securities Acts, with respect to the qualification for distribution
effected pursuant to this Section 2, and each underwriter, if any, and each
person who controls any underwriter within the meaning of the Securities Acts,
against all expenses, claims, losses, damages or liabilities (or actions in
respect thereof), which may be incurred or arise by reason of the preliminary
or the final prospectus containing any misrepresentation (as defined in the
Securities Acts) or containing any information or statement that is untrue with
respect to a material fact (as defined in the Securities Acts) or by reasons of
the omission to state therein any fact required to be stated therein or
necessary to make the statements therein not misleading in the circumstances
they were made, or any violation by BioChem under the Securities Acts in
connection with any such qualification for distribution, and BioChem will
reimburse NAVA, each of its officers and directors and each person controlling
NAVA, each such underwriter and each person who controls any such underwriter,
for any legal and any other expenses reasonably


<PAGE>   61

                                      -25-

incurred in connection with investigating, preparing or defending any such
claim, loss, damage, liability or action, provided that BioChem will not be
liable in any such case to the extent that any such claim, loss, damage,
liability or expense arises out of or is based on any untrue statement or
omission or alleged untrue statement or omission, made in reliance upon and in
conformity with written information furnished to BioChem by an instrument duly
executed by NAVA or any such controlling person or underwriter expressly for
use therein.

        (b) NAVA will indemnify BioChem, each of its directors and officers,
each underwriter, if any, of BioChem's securities covered by such a
qualification for distribution and each person who controls BioChem or such
underwriter within the meaning of the Securities Acts, against all expenses,
claims, losses, damages or liabilities (or actions in respect thereof), which
may be incurred or arise by reason of the preliminary or the final prospectus
containing any misrepresentation (as defined in the Securities Acts) or
containing any information or statement that is untrue with respect to a
material fact (as defined in the Securities Acts) or by reason of the omission
to state therein any fact required to be stated therein or necessary to make
the statements therein not misleading in the circumstances they were made and
will reimburse BioChem, each such underwriter and each person who controls any
such underwriter, for any legal and any other expenses reasonably incurred in
connection with investigating, preparing or defending any such claim, loss,
damage, liability or action, in each case to the extent, but only the extent,
that such untrue statement (or alleged untrue statement) or omission (or
alleged omission) is made in such prospectus,


<PAGE>   62

                                      -26-


offering circular or other document in reliance upon and in conformity with
written information furnished to BioChem by an instrument duly executed by NAVA
expressly for use therein.

        (c) Each party entitled to indemnification under this Section 2.6 (the
"Indemnified Party") shall give notice to the party required to provide
indemnification (the "Indemnifying Party") promptly after such Indemnified
Party has actual knowledge of any claim as to which indemnity may be sought,
and shall permit the Indemnifying Party to assume the defense of any such claim
or any litigation resulting therefrom, provided that counsel for the
Indemnifying Party, who shall conduct the defense of such claim or litigation,
shall be approved by the Indemnified Party (whose approval shall not
unreasonably be withheld), and the Indemnified Party may participate in such
defense at such party's expense, and provided further that the failure of any
Indemnified Party to give notice as provided herein shall not relieve the
Indemnifying Party of its obligations under this Section 2 unless the failure
to give such notice is materially prejudicial to an Indemnifying Party's
ability to defend such action. No Indemnifying Party, in the defense of any
such claim or litigation, shall, except with the consent of each Indemnified
Party, consent to entry of any judgment or enter into any settlement which does
not include as an unconditional term thereof the giving by the claimant or
plaintiff to such Indemnified Party of a release from all liability in respect
of such claim or litigation.

        2.7. Information by NAVA. It shall be a condition precedent to the
obligations of BioChem to effect a qualification for distribution pursuant to
this Section 2


<PAGE>   63

                                      -27-

that NAVA shall furnish to BioChem such information regarding NAVA, the
Securities and the distribution proposed by NAVA as BioChem may request in
writing and as shall be required in connection with any qualificatior for
distribution referred to in this Section 2.

        2.8. No Transfer of Rights. The rights to cause BioChem to qualify for
distribution securities granted to NAVA under Sections 2.2 and 2.3 are not
assignable in connection with any transfer or assignment of Securities by NAVA
o: otherwise.

        2.9. Limitation on Injunctions. NAVA shall not have any right to obtain
or seek an injunction restraining or otherwise delaying any distribution as the
result of any controversy that might arise with respect to the interpretation
or implementation of the provisions of this Section 2.



<PAGE>   1

                                                                EXHIBIT 4.B

                     AMENDMENT TO SHARE PURCHASE AGREEMENT

        THIS AMENDMENT TO SHARE PURCHASE AGREEMENT (this "Amendment"), dated as
of January 8, 1998 is entered into by and between North American Vaccine, Inc.,
a Canadian corporation, ("NAVA") and BioChem Pharma Inc., (successor to IAF
BioChem International Inc.) a corporation organized under the laws of Canada
("BioChem").

                                    RECITALS

        WHEREAS, NAVA and BioChem entered into a Share Purchase Agreement on
January 17, 1990 (the "Share Purchase Agreement "); and

        WHEREAS, pursuant to Section 8.1 of the Share Purchase Agreement, NAVA
granted to BioChem certain registration rights with respect to common shares,
no par value, of NAVA ("Common Shares"), which registration rights were set
forth in Schedule 4 to the Share Purchase Agreement; and

        WHEREAS, the parties entered into that certain Amendment to Share
Purchase Agreement (the "First Amendment") dated June 20, 1994, whereby
Schedule 4 to the Share Purchase Agreement was amended to, among other things,
amend the demand registration right held by BioChem for its NAVA Common Shares;
and

        WHEREAS, BioChem's one remaining demand registration right is scheduled
to expire on January 17, 1998; and

        WHEREAS, the parties desire to extend the term of BioChem's one
remaining demand registration right for its NAVA Common Shares for an
additional three(3) years; and

        WHEREAS, the parties desire to set forth their agreements and
understanding with respect to these matters.

        NOW, THEREFORE, in consideration of the foregoing, of the mutual
promises herein contained, and of other good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledged, the parties hereto,
intending to be legally bound, hereby agree as follows:

I.  MODIFICATION AND AMENDMENT

        1.1 Section 1.2(a)(vi) of Schedule 4 to the Share Purchase Agreement
shall be and hereby is revised in its entirety to read as follows:

               "(vi) after January 17, 2001."

II. MISCELLANEOUS

<PAGE>   2

        2.1 Except as set forth in this Amendment, all provisions of the Share
Purchase Agreement, as amended by the First Amendment, shall remain in full
force and effect without modification or amendment. Unless otherwise defined in
this Amendment, all capitalized terms used herein shall be as defined in the
Share Purchase Agreement, as amended.

        2.2 This Amendment may be executed in any number of counterparts, each
of which shall be deemed an original but all of which together shall constitute
one and the same instrument.

        2.3 This Amendment shall be deemed to have been made in the Province of
Quebec and shall be interpreted in accordance with and governed by the laws of
Quebec and the laws of Canada applicable therein.  The parties hereto have
requested that this Amendment and all agreements and documents related thereto
be drafted in the English language.  Les parties aux presentes ont exige que la
presente convention et tout document accessoire soient redige en anglais
seulement.

        2.4 If any provision of this Amendment is held contrary to any federal,
provincial, state or local law, the invalidity of such provision shall not
affect any other provision of this Amendment, and the remaining provisions
hereof shall continue in full force and effect and unmodified thereby.  Any
restriction or obligation contained herein which cannot be enforced to its full
extent shall be enforced to the maximum extent permitted by law.

        IN WITNESS WHEREOF, the parties have caused this Amendment to Share
Purchase Agreement to be executed by their duly authorized officers as of the
day and year first above written.


                                 NORTH AMERICAN VACCINE, INC.

                                 By:    /s/Daniel J. Abdun-Nabi
                                        -----------------------

                                 Name:  Daniel J. Abdun-Nabi
                                        --------------------

                                 Title: Sr. Vice President-Legal Affairs
                                        --------------------------------

                                 BIOCHEM PHARMA INC.

                                 By:    /s/ Francois Legault
                                        --------------------

                                 Name:  Francois Legault
                                        ----------------

                                 Title: Ex. V.P. Investments and Subsidiaries
                                        -------------------------------------

                                        /s/ Charles A. Tessier
                                        Charles A. Tessier
                                        V.P. Legal & Sec.



<PAGE>   1
                                   EXHIBIT 5
           TO SCHEDULE 13-D AMENDMENT - NORTH AMERICAN VACCINE, INC.
                 DIRECTORS AND OFFICERS OF BIOCHEM PHARMA INC.

<TABLE>
<CAPTION>


                        BUSINESS OR         PRINCIPAL
                        RESIDENTIAL       OCCUPATION OR
NAME                      ADDRESS          EMPLOYMENT           COMPANY            CITIZENSHIP
===============================================================================================
<S>                     <C>               <C>                   <C>                <C>
Frederick J.            275 Armand-       Chief Financial       BioChem Pharma     Canadian
Andrew                  Frappier          Officer               Inc.
                        Boulevard
                        Laval, Quebec
                        H7V 4A7
- -----------------------------------------------------------------------------------------------
Francesco Bellini,      275 Armand-       Chief Executive       BioChem Pharma     Canadian
Ph.D.                   Frappier          Officer               Inc.
                        Boulevard
                        Laval, Quebec
                        H7V 4A7
- -----------------------------------------------------------------------------------------------
Bernard Canavan,        10700 Beach Road  Retired Executive     N/A                American
M.D.                    Suite 2 North
                        Jupiter Island,
                        Florida 33469
- -----------------------------------------------------------------------------------------------
Gervais Dionne,         275 Armand-       Executive Vice        BioChem Pharma     Canadian
Ph.D.                   Frappier          President,            Inc.
                        Boulevard         Research and
                        Laval, Quebec     Development
                        H7V 4A7
- -----------------------------------------------------------------------------------------------
Jean-Louis              800 Rene-         Chairman of the       Bombardier Inc.    Canadian
Fontaine                Levesque          Board
                        Boulevard West    Vice President,
                        29th Floor        Corporate Affairs
                        Montreal, Quebec
                        H3B 1Y8
- -----------------------------------------------------------------------------------------------
Jean-Francois           222 Berkeley      General Partner       Atlas Venture      French
Formela, M.D.           Avenue
                        Boston,
                        Massachusetts
                        02116
- -----------------------------------------------------------------------------------------------
The Honorable           1155 Rene-        Partner               Stikeman, Elliott  Canadian
James A. Grant,         Levesque
P.C., Q.C.              Boulevard West
                        Montreal, Quebec
                        H3B 3V2
- -----------------------------------------------------------------------------------------------
Roderick L. Henry       1800 McGill       President             Henrod             Canadian
                        College Avenue                          Investments Inc.
                        Suite 2400
                        Montreal, Quebec
                        H3A 3J6
- -----------------------------------------------------------------------------------------------
Jacques R.              275 Armand-       President and         BioChem Pharma     Canadian
Lapointe                Frappier          Chief Operating       Inc.
                        Boulevard         Officer
                        Laval, Quebec
                        H7V 4A7
- -----------------------------------------------------------------------------------------------
</TABLE>
<PAGE>   2
                                                                               2

Exhibit 5
Schedule 13D Amendment - North American Vaccine, Inc.

<TABLE>
<CAPTION>
                        BUSINESS OR         PRINCIPAL
                        RESIDENTIAL       OCCUPATION OR
NAME                      ADDRESS          EMPLOYMENT           COMPANY            CITIZENSHIP
===============================================================================================
<S>                     <C>               <C>                   <C>                <C>
Francois Legault        275 Armand-       Executive Vice        BioChem Pharma     Canadian
                        Frappier          President,            Inc.
                        Boulevard         Investments and
                        Laval, Quebec     Subsidiaries
                        H7V 4A7
- -----------------------------------------------------------------------------------------------
Guy Lord                275 Armand-       Senior Vice           BioChem Pharma     Canadian
                        Frappier          President,            Inc.
                        Boulevard         Corporate Affairs
                        Laval, Quebec     and Secretary
                        H7V 4A7
- -----------------------------------------------------------------------------------------------
Michel Perron           2080 Rene-        Chairman of the       Somiper Inc.       Canadian
                        Levesque          Board and Chief
                        Boulevard West    Executive Officer
                        Montreal, Quebec
                        H3H 1R6
- -----------------------------------------------------------------------------------------------
J. Robert S.            Simcoe Hall --    President             University of      Canadian
Prichard, Ph.D.         Room 206                                Toronto
                        27 King's College
                        Circle
                        Toronto, Ontario
                        M5S 1A1
- -----------------------------------------------------------------------------------------------
Guy Savard              1250 Rene-        Vice Chairman         Merrill Lynch      Canadian
                        Levesque          and Chairman          Canada Inc.
                        Boulevard West    Quebec Operations
                        Suite 3100
                        Montreal, Quebec
                        H3B 4W8
- -----------------------------------------------------------------------------------------------
Charles A. Tessier      275 Armand-       Vice President,       BioChem Pharma     Canadian
                        Frappier          Legal Affairs and     Inc.
                        Boulevard         General Counsel
                        Laval, Quebec
                        H7V 4A7
- -----------------------------------------------------------------------------------------------
Gerard Veilleux         751, Square       President             Power              Canadian
                        Victoria                                Communications
                        Montreal, Quebec                        Inc.
                        H2Y 2J3
- -----------------------------------------------------------------------------------------------
</TABLE>


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