AVIRON
S-3, 2000-09-01
BIOLOGICAL PRODUCTS, (NO DIAGNOSTIC SUBSTANCES)
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<PAGE>   1
     AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON SEPTEMBER 1, 2000
                                                  Registration No. 333-
================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                    FORM S-3
                             REGISTRATION STATEMENT
                                      UNDER
                           THE SECURITIES ACT OF 1933
                                     AVIRON
             (Exact name of registrant as specified in its charter)

             DELAWARE                                        77-0309686
  (State or other jurisdiction of                         (I.R.S. Employer
  incorporation or organization)                       Identification Number)

                            297 NORTH BERNARDO AVENUE
                         MOUNTAIN VIEW, CALIFORNIA 94043
                                 (650) 919-6500
  (Address, including zip code, and telephone number, including area code, of
                   Registrant's principal executive offices)

                                 C. BOYD CLARKE
                      PRESIDENT AND CHIEF EXECUTIVE OFFICER
                                     AVIRON
                            297 NORTH BERNARDO AVENUE
                         MOUNTAIN VIEW, CALIFORNIA 94043
                                 (650) 919-6500
 (Name, address, including zip code, and telephone number, including area code,
                             of agent for service)

                                    Copy to:
                             ROBERT J. BRIGHAM, ESQ.
                               COOLEY GODWARD LLP
                              FIVE PALO ALTO SQUARE
                               3000 EL CAMINO REAL
                           PALO ALTO, CALIFORNIA 94306
                                 (650) 843-5000

          APPROXIMATE DATE OF COMMENCEMENT OF PROPOSED SALE TO PUBLIC:
As soon as practicable after the effective date of this Registration Statement.

    If any of the securities being registered on this Form are to be offered on
a delayed or continuous basis pursuant to Rule 415 under the Securities Act of
1933, as amended, other than securities offered only in connection with dividend
or interest reinvestment plans, check the following box. [X]

    If this Form is filed to register additional securities for an offering
pursuant to Rule 462(b) under the Securities Act, please check the following box
and list the Securities Act registration statement number of the earlier
effective registration statement for the same offering. [ ]

    If this Form is to be a post-effective amendment filed pursuant to Rule
462(c) under the Securities Act, check the following box and list the Securities
Act registration statement of the earlier effective registration statement for
the same offering. [ ]

    If delivery of the prospectus is expected to be made pursuant to Rule 434,
please check the following box. [ ]

                         CALCULATION OF REGISTRATION FEE

<TABLE>
<CAPTION>
---------------------------------------------------------------------------------------------------------------
                                                         PROPOSED MAXIMUM     PROPOSED MAXIMUM    AMOUNT OF
                                       AMOUNT TO BE     OFFERING PRICE PER       AGGREGATE       REGISTRATION
TITLE OF SHARES TO BE REGISTERED        REGISTERED           SHARE(1)        OFFERING PRICE(1)       FEE
---------------------------------------------------------------------------------------------------------------
<S>                                  <C>                <C>                  <C>                 <C>
Common stock, $0.001 par value...    1,038,235 shares       $39.625           $41,140,062         $10,861
---------------------------------------------------------------------------------------------------------------
</TABLE>

(1) Estimated solely for the purpose of calculating the registration fee
    pursuant to Rule 457(c) under the Securities Act of 1933 on the basis of the
    high and low prices of Aviron's common stock on August 25, 2000 as quoted on
    the Nasdaq National Market. It is not known how many shares will be
    purchased under this Registration Statement or at what price shares will be
    purchased.

THE REGISTRANT HEREBY AMENDS THIS REGISTRATION STATEMENT ON SUCH DATE OR DATES
AS MAY BE NECESSARY TO DELAY ITS EFFECTIVE DATE UNTIL THE REGISTRANT SHALL FILE
A FURTHER AMENDMENT THAT SPECIFICALLY STATES THAT THIS REGISTRATION STATEMENT
SHALL THEREAFTER BECOME EFFECTIVE IN ACCORDANCE WITH SECTION 8(a) OF THE
SECURITIES ACT OF 1933 OR UNTIL THE REGISTRATION STATEMENT SHALL BECOME
EFFECTIVE ON SUCH DATE AS THE SECURITIES AND EXCHANGE COMMISSION, ACTING
PURSUANT TO SAID SECTION 8(a), MAY DETERMINE.

<PAGE>   2

                 SUBJECT TO COMPLETION, DATED SEPTEMBER 1, 2000

The information in this prospectus is not complete and may be changed. The
selling stockholders may not sell these securities until the Registration
Statement filed with the Securities and Exchange Commission is effective. This
prospectus is not an offer to sell these securities and is not soliciting an
offer to buy these securities in any state where the offer or sale is not
permitted.

                                   PROSPECTUS

                                     AVIRON

                                1,038,235 SHARES

                                  COMMON STOCK

    These shares of common stock are being offered by the selling stockholders,
identified in this prospectus. The selling stockholders may sell these shares
from time to time on the over-the-counter market in regular brokerage
transactions, in transactions directly with market makers or in certain
privately negotiated transactions. For additional information on the methods of
sale, you should refer to the section entitled "Plan of Distribution" on page
11. We are not selling any shares of our common stock under this prospectus and
will not receive any portion of the proceeds from the sale of these shares.

    Each of the selling stockholders may be deemed to be an "Underwriter," as
such term is defined in the Securities Act of 1933.

    The selling stockholders may sell their Aviron common stock in one or more
transactions on the NASDAQ National Market at prevailing market prices or at
privately negotiated prices. The selling stockholders may sell their shares
directly or through agents, brokers, dealers or underwriters. The selling
stockholders will pay for underwriting discounts and selling commissions related
to the sale of shares. We will pay for all other expenses related to such sales.

    Aviron's common stock is traded on the Nasdaq National Market under the
symbol "AVIR". On August 31, 2000, the last reported sale price for our common
stock on the Nasdaq National Market was $45.00 per share.

    INVESTING IN SECURITIES ISSUED BY AVIRON INVOLVES CERTAIN RISKS. SEE "RISK
FACTORS" BEGINNING ON PAGE 4.

    NEITHER THE SECURITIES AND EXCHANGE COMMISSION NOR ANY STATE SECURITIES
COMMISSION HAS APPROVED OR DISAPPROVED OF THE SECURITIES OR PASSED UPON THE
ACCURACY OR ADEQUACY OF THIS PROSPECTUS. ANY REPRESENTATION TO THE CONTRARY IS A
CRIMINAL OFFENSE.

                 THE DATE OF THIS PROSPECTUS IS           , 2000

<PAGE>   3

                                TABLE OF CONTENTS

<TABLE>
<CAPTION>
                                                                     PAGE NUMBER
                                                                     -----------
<S>                                                                  <C>
WHERE YOU CAN FIND MORE INFORMATION........................................1
SUMMARY....................................................................2
THE COMPANY................................................................2
RISK FACTORS...............................................................4
SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS..........................9
USE OF PROCEEDS............................................................9
SELLING STOCKHOLDERS......................................................10
PLAN OF DISTRIBUTION......................................................11
LEGAL MATTERS.............................................................12
EXPERTS...................................................................12
</TABLE>

    You should rely only on the information contained in, or incorporated into
this prospectus. We have not authorized anyone to provide you with information
different from that contained in this prospectus. The information contained in
this prospectus is accurate only as of the date of this prospectus, regardless
of the time of delivery of this prospectus or of any sale of common stock.

    We own or have rights to trademarks or trade names that we use in
conjunction with the operation of our business. We own the FluMist trademark in
the United States. This prospectus also includes trademarks owned by other
parties.

                       WHERE YOU CAN FIND MORE INFORMATION

    We are a reporting company and file annual, quarterly and current reports,
proxy statements and other information with the Securities and Exchange
Commission, or the SEC. You may read and copy these reports, proxy statements
and other information at the SEC's public reference rooms in Washington, D.C.,
New York, NY and Chicago, IL. You can request copies of these documents by
writing to the SEC and paying a fee for the copying cost. Please call the SEC at
1-800-SEC-0330 for more information about the operation of the public reference
rooms. Our SEC filings are also available at the SEC's Web site at
"http://www.sec.gov". In addition, you can read and copy our SEC filings at the
office of the National Association of Securities Dealers, Inc. at 1735 K Street,
Washington, D.C. 20006.

    The SEC allows us to "incorporate by reference" information that we file
with them, which means that we can disclose important information to you by
referring you to those documents. The information incorporated by reference is
an important part of this prospectus, and information that we file later with
the SEC will automatically update and supersede this information. Further, all
filings we make under the Securities Exchange Act after the date of the initial
registration statement and prior to effectiveness of the registration statement
shall be deemed to be incorporated by reference into this prospectus. We
incorporate by reference the documents listed below and any future filings we
will make with the SEC under Section 13(a), 13(c), 14 or 15(d) of the Securities
Exchange Act of 1934:

    1.  Our Current Report on Form 8-K dated January 11, 2000, filed with the
        SEC on January 14, 2000;

    2.  Our Annual Report on Form 10-K for the year ended December 31, 1999,
        filed with the SEC on March 8, 2000, and amended by a Form 10-K/A filed
        with the SEC on April 3, 2000 and April 28, 2000;

    3.  Our Definitive Proxy Statement dated May 4, 2000, filed with the SEC on
        May 4, 2000, in connection with our 2000 Annual Meeting of Stockholders;

    4.  Our Quarterly Reports on Form 10-Q for the quarters ended March 31, 2000
        and June 30, 2000, filed with the SEC on May 15, 2000 and August 11,
        2000, respectively;

    5.  Our Current Report on Form 8-K dated June 12, 2000, filed with the SEC
        on June 13, 2000; and

    6.  The description of our common stock set forth in our Registration
        Statement on Form 8-A, filed with the SEC on July 16, 1996.

We will provide to you at no cost a copy of any and all of the information
incorporated by reference into the registration statement of which this
prospectus is a part. You may make a request for copies of this information in
writing or by telephone. Requests should be directed to:

                                     Aviron
                          Attention: Investor Relations
                            297 North Bernardo Avenue
                             Mountain View, CA 94043
                                 (650) 919-6500



                                       1
<PAGE>   4

                                     SUMMARY

This prospectus contains forward-looking statements which involve risks and
uncertainties. Our actual results could differ materially from those anticipated
in these forward-looking statements as a result of certain factors appearing
under "Risk Factors" and elsewhere in this prospectus.

The following summary does not contain all the information that may be important
to you. You should read the entire prospectus, including the financial
statements and other information incorporated by reference in this prospectus,
before making an investment decision.

                                   THE COMPANY

    We are a biopharmaceutical company focused on the prevention of disease
through innovative vaccine technology. We are currently focusing our product
development and commercialization efforts on our lead product candidate,
FluMist, an investigational live virus vaccine for influenza delivered as a
nasal spray. Our goal is to become a leader in the discovery, development,
manufacture and marketing of innovative development vaccines which are safe,
effective and economical enough to merit their use in immunization programs
targeting the general population. Our vaccine programs are based both on
techniques for producing weakened live virus vaccines and on our proprietary
genetic engineering technologies. Live virus vaccines, including those for
smallpox, polio, measles, mumps, rubella and chicken pox, have had a long record
of preventing disease.

    According to the Centers for Disease Control and Prevention, or CDC,
epidemics of influenza occur during the winter months nearly every year and are
responsible for an average of approximately 20,000 deaths per year in the United
States. Influenza viruses also can cause global epidemics of disease during
which rates of illness and death from influenza-related complications can
increase dramatically. Influenza viruses cause disease in all age groups. Rates
of infection are highest among children, but rates of serious illness and death
are highest among persons age 65 or older, and persons of any age who have
medical conditions that place them at high risk for complications from
influenza.

    FluMist is designed to prevent influenza. We are developing and intend to
commercialize FluMist primarily in collaboration with our partner Wyeth Lederle
Vaccines, a business unit of the pharmaceutical division of American Home
Products Corporation, or AHP. FluMist has been shown to provide a high
protection rate against influenza in Phase 3 clinical trials in children and
healthy adults. In a separate trial conducted in healthy working adults,
reductions in days of illness, antibiotic use, health resource use and missed
work because of illness were observed across several illness definitions. Based
on our clinical data, we intend to submit a Biologics License Application, or
BLA, to the U.S. Food and Drug Administration, or FDA, during the fourth quarter
of 2000.

    Influenza vaccination rates for healthy children are substantially below
those for the general population. In addition, the majority of healthy adults
currently do not receive the influenza vaccine. We believe that there are
significant market opportunities for FluMist in these two populations.

    We believe FluMist can achieve significant market acceptance because:

    -   In clinical trials, FluMist provided protection rates as high as 93% in
        healthy children and 85% in healthy adults;

    -   FluMist is a nasal spray which pediatricians, parents and vaccine
        recipients may find as an attractive new way to prevent influenza;

    -   In a large clinical trial, FluMist helped reduce the incidence of middle
        ear infections in children and the associated antibiotic use;

    -   As noted in a recent article in the Journal of Pediatrics, FluMist is a
        weakened live virus vaccine which triggers an immune response similar to
        the natural immune response to influenza, while the response to the flu
        shot is more narrowly focused;

    -   FluMist stimulates immunity in the nose and throat, the point of contact
        for airborne infections such as influenza, as well as in the
        bloodstream; and

    -   FluMist has been administered to more than 13,000 people with no serious
        adverse events associated with use of the vaccine.

    The FDA notified us in 1998 that, in order to support a BLA filing for
FluMist, we must demonstrate the clinical equivalence between FluMist produced
in our new manufacturing facility located in Pennsylvania and FluMist used in
our Phase 3 trials. We must also provide additional data on manufacturing
validation and stability. In June 1999, we reported the results of a clinical
trial that we believe demonstrated the required clinical equivalence. We are in
the process of completing the manufacturing validation exercises, stability
studies and documentation we believe necessary to support a BLA for FluMist,
which we intend to submit during the fourth quarter of 2000.

    The current formulation of FluMist requires freezer storage throughout
distribution. Because international markets do not have distribution channels
well suited to the sale of frozen vaccines, Wyeth Lederle has initiated a Phase
2 clinical trial outside of the United States for our second generation
refrigerator stable, or liquid, formulation of FluMist.



                                       2
<PAGE>   5

    We also have a number of other vaccines in various stages of development:

    -   a parainfluenza virus type 3 vaccine to prevent the most common cause of
        croup, a respiratory infection in infants, for which we have completed a
        successful Phase 2 clinical trial;

    -   an Epstein-Barr virus vaccine to prevent infectious mononucleosis for
        which our collaborative partner, SmithKline Beecham Biologicals S.A.,
        has completed a successful Phase 1 clinical trial; and

    -   a vaccine for cytomegalovirus, the leading infectious cause of birth
        defects, for which clinical testing began during the second quarter of
        2000.

     We are also using our proprietary vaccine design technologies to discover
     new vaccines, including vaccine candidates for herpes simplex virus type 2,
     the virus responsible for genital herpes, and respiratory syncytial virus,
     a virus responsible for a severe lower respiratory infection in infants and
     young children.

    We were incorporated in California in April 1992, and reincorporated in
Delaware in November 1996. Our executive offices are located at 297 North
Bernardo Avenue, Mountain View, California 94043 and our telephone number is
(650) 919-6500. Aviron's World Wide Web address is http://www.aviron.com.
Information contained in our World Wide Web site should not be considered to be
part of this prospectus.



                                       3
<PAGE>   6

                                  RISK FACTORS


    You should carefully consider the risks described below before making an
investment decision. The risks described below are not the only ones facing our
company. Additional risks not presently known to us or that we currently deem
immaterial may also impair our business operations.

    Our business, financial condition or results of operations could be
materially adversely affected by any of these risks. The trading price of our
common stock could decline due to any of these risks, and you may lose all or
part of your investment.

    This prospectus also contains forward-looking statements that involve risks
and uncertainties. Our actual results could differ materially from those
anticipated in these forward-looking statements as a result of certain factors,
including the risks faced by us described below and elsewhere in this
prospectus.

RISKS RELATED TO FLUMIST

    For the foreseeable future, the risks relating to Aviron are primarily those
related to the development and commercialization of FluMist. All of our
potential near-term revenues are dependent on the commercialization of FluMist.
Because of the seasonality of influenza, FluMist must be available in the third
or fourth quarter of the year for us to achieve revenues for that season. Delay
in availability of FluMist in the initial year of commercialization or in
subsequent years could cause us to lose revenues for an entire influenza season
and require us to raise additional capital to cover the costs of additional
research and development, related expenses and ongoing fixed costs.

POSTPONING THE SUBMISSION OF OUR APPLICATION TO THE FDA FOR FLUMIST WILL DELAY
THE COMMERCIALIZATION OF FLUMIST.

    In 1998, we submitted an application for FluMist, which was not accepted for
filing by the FDA. Additional information required before we resubmit our
application includes data on manufacturing validation, stability and clinical
equivalence. If our manufacturing validation exercises and studies to confirm
sufficient shelf-life stability are not successful, or if our facilities
validation is delayed, or we encounter additional problems, we will postpone our
submission beyond 2000, which will delay commercialization of FluMist.

IF THE FDA FINDS THAT OUR APPLICATION FOR FLUMIST DOES NOT SUPPORT APPROVAL, OR
IF ITS INSPECTORS FIND THAT OUR MANUFACTURING FACILITIES ARE NOT ADEQUATE,
COMMERCIALIZATION OF FLUMIST MAY BE DELAYED BY ONE OR MORE INFLUENZA SEASONS.

    Approval risk related to manufacturing. If the FDA finds that the
validation, clinical or other required data in our application is insufficient,
it could refuse to accept our application for filing or could require corrective
action or additional data which could delay or prevent approval. The FDA is
likely to inspect each of the facilities involved in manufacturing FluMist. FDA
inspectors may find deficiencies in the facilities or processes that may lead to
delay in FluMist approval or prevent it from being approved at all.

    Celltech Medeva, or Medeva, the international marketing arm of Celltech
Group, plc, notified us that it received a warning letter from the FDA regarding
their United Kingdom facility where several key stages of the FluMist
manufacturing process take place. Some of the comments in the letter referred to
the general utility systems in the facility, such as water and clean steam,
which are used to prepare supplies used in the manufacture of FluMist. We have
been informed by Medeva that it is taking the necessary steps to bring its
systems and facility into compliance, and it is working with the FDA to fulfill
that objective. While we believe Medeva has taken the necessary steps to bring
the relevant general utility systems into compliance, we have also begun to
implement plans to eliminate our dependence on these utilities in connection
with our planned fourth quarter 2000 BLA submission. Those plans, which will
require FDA approval, involve the use of disposable supplies, instead of relying
on the shared utility systems at Medeva.

    Approval risk related to FluMist indications and claims. We are initially
seeking FDA approval for use of FluMist in children and healthy adults. The FDA
may not find our clinical data adequate to support use in any particular group
and may exclude any segment of the population. The FDA may request additional
clinical data to support the safety of FluMist. We may be required to commence
and complete additional clinical trials to generate additional data to support
product approval for one or more of our target populations, which may lead to
substantial delay in FluMist approval or prevent it from being approved for any
of those population segments.

IF WE ARE UNABLE TO PERFORM THE COMPLEX ANNUAL UPDATE OF THE FLUMIST FORMULATION
FOR NEW INFLUENZA STRAINS IN A TIMELY MANNER, OUR SALES FOR THAT YEAR WILL BE
LIMITED OR WE MAY HAVE NO SALES AT ALL.

    Early each year, the FDA determines which strains will be included in the
upcoming season's influenza vaccines. After the FDA makes its decision, we will
have approximately six months to include the selected strains and manufacture
FluMist for use in the upcoming influenza season. The major factors that may
delay availability of FluMist each year are:

    - The FDA may delay its selection of strains for a given influenza season.

    - We may experience difficulty or delay in the technically demanding process
      we follow each year to update the formulation of FluMist.

    - The FDA could require as a release test a brief clinical trial designed to
      show the safety and activity of the vaccine including the new strains
      selected for that particular year.



                                       4
<PAGE>   7

IF WE HAVE DIFFICULTIES WITH OUR MANUFACTURING PROCESS, WE MAY NOT HAVE
SUFFICIENT QUANTITIES OF VACCINE.

     We may not have sufficient quantities of vaccine in time to assure
availability for the season due to problems with updated strains or performance
of suppliers or contract manufacturers. Following inoculation with our updated
strains, bulk vaccine is harvested from special hens' eggs. This is a
labor-intensive process which must be conducted under strict controls and tight
timelines. We are dependent on our contract manufacturer for successful
staffing, training and supervision for this process. We are currently dependent
on a single supplier for an adequate and timely supply of eggs.

     We may have difficulty with the blending, filling and packaging of FluMist.
The bulk vaccine for three strains of influenza must be diluted and blended
together prior to filling the nasal spray device. This process must be conducted
under strict controls and tight timelines. We depend upon a single supplier for
our nasal spray device. We also depend upon our packaging contractor for
packaging of the vaccine. The vaccine is subject to strict quality control
testing during production and prior to release. Any quality control failures
could lead to a reduction in the available supply of FluMist.

IF THE MARKET DEMAND FOR FLUMIST EXCEEDS OUR MANUFACTURING CAPACITY, OUR REVENUE
MAY BE LIMITED.

     We may be capacity constrained in our supply of vaccine. In order to secure
future production capacity, we may extend and expand existing arrangements,
collaborate with other third parties, or establish additional manufacturing
facilities. Using an alternative supplier or building a new facility would
require a substantial amount of funds and additional clinical trials and
testing. We cannot be sure that an additional source of supply will be
established on a timely basis, or that we will have or be able to obtain funds
sufficient for building or equipping a new facility.

THE SUCCESS OF FLUMIST IS HIGHLY DEPENDENT ON OUR PARTNER, WYETH LEDERLE, FOR
MARKETING, PROMOTION, SALES AND DISTRIBUTION ACTIVITIES.

     We have entered into an exclusive agreement with Wyeth Lederle to
co-promote, sell, and distribute FluMist. We believe that for FluMist to be
widely adopted, the efforts of an experienced pharmaceutical sales force are
needed. If Wyeth Lederle fails to devote appropriate resources to promote, sell,
and distribute FluMist, sales of FluMist could be reduced. Distribution of
FluMist will be challenging for several reasons. First, influenza vaccine is a
seasonal product with a shipping period between August and January. Second,
FluMist is a frozen product and must remain frozen prior to use. It must be
maintained under recommended frozen storage conditions. Although Wyeth Lederle
has a distribution system that supports frozen vaccines, if it does not manage
these distribution challenges our revenues could be reduced.

     Wyeth Lederle also will participate in the development, manufacturing,
promoting, and selling of a liquid formulation of FluMist, which will be
particularly important if FluMist is to be accepted outside of the United
States. If Wyeth Lederle does not devote sufficient resources to the development
and commercialization of this formulation, its commercial availability will be
delayed.

     If Wyeth Lederle breaches or terminates its agreement with us or otherwise
fails to conduct their FluMist related activities in a timely manner or if there
is a dispute about our or their respective obligations, we may need to seek
another partner. If any of these events occurs, revenues associated with
milestone payments or FluMist commercialization could be delayed, reduced or be
substantially more expensive for us to achieve.

IF MEDICAL ADVISORY BODIES, DOCTORS, AND OTHER HEALTH CARE PROVIDERS DO NOT
RECOMMEND FLUMIST ITS MARKET OPPORTUNITY WILL BE LIMITED.

     We believe recommendations from advisory bodies such as the Advisory
Committee on Immunization Practices, or ACIP, of the CDC, and the American
Academy of Pediatrics, or AAP, will be important to encourage doctors and other
healthcare providers to recommend FluMist. If these bodies do not recommend
FluMist, the product's market opportunity will be limited. We will also need to
educate doctors and other healthcare advisors of the safety and clinical
efficacy of FluMist and its potential advantages over other influenza vaccines.

WHETHER OR NOT DOCTORS, OTHER HEALTH CARE PROVIDERS AND MEDICAL ADVISORY BODIES
RECOMMEND FLUMIST, IF THE MARKET DOES NOT ACCEPT FLUMIST, OUR SALES WILL BE
REDUCED.

     FluMist acceptance may be limited by a number of factors, including:

     - perceived effectiveness of competing influenza vaccines, including the
       shot;

     - unfavorable publicity concerning other vaccines;

     - pricing of FluMist;

     - broad accessibility to FluMist;

     - reimbursement polices of government and third-party payors;

     - side effects, such as the runny nose, sore throat or fever seen in some
       clinical trial participants; and

     - the requirement of frozen storage capacity by those distributing and
       administering the vaccine.



                                       5
<PAGE>   8

WE FACE COMPETITION FROM COMPANIES WITH SUBSTANTIAL FINANCIAL, TECHNICAL, AND
MARKETING RESOURCES, WHICH COULD SERIOUSLY LIMIT OUR FUTURE REVENUES FROM
FLUMIST.

     FluMist will be competing against the flu shot, which is sold by large
pharmaceutical companies, including Wyeth Lederle and Medeva.

     We also operate in a rapidly evolving field. Other companies are working to
improve the efficacy of flu shots. In addition, we are aware of efforts to
develop non-injectable influenza vaccines that would be more directly
competitive with FluMist. For example:

     - A nasally administered inactivated vaccine is being developed by
       Biovector Therapeutics, S.A. and Biochem Pharma, Inc. which has been
       licensed to SmithKline Beecham; and

     - A nasally administered live influenza vaccine has been developed and used
       in Russia.

     In 1999, the FDA approved two new products for the treatment of influenza:
zanamivir and oseltamivir. Zanamivir is marketed as Relenza and is sold by Glaxo
Wellcome plc and oseltamivir is marketed as Tamiflu and is sold by Roche
Holdings AG. These products inhibit the ability of the influenza virus to
replicate. Both zanamivir, delivered via an inhaled powder, and oseltamivir, a
pill, were approved for influenza treatment, but neither are approved for the
prevention of influenza. When administered within two days of contracting
influenza, zanamivir and oseltamivir may reduce the duration of influenza by
approximately one day. Clinical data also has shown that taking zanamivir or
oseltamivir daily for a period of time during the influenza season can have a
preventative effect.

THE FLUMIST MASTER DONOR STRAINS ARE NOT PROTECTED BY PATENTS AND IF THE STRAINS
ARE DUPLICATED, THIRD PARTIES MAY BE ABLE TO DEVELOP, MARKET AND SELL A
COMPETING VACCINE.

     We have no issued patents covering the FluMist master donor strains. Our
rights to the master donor strains are substantially based on (1) an exclusive
worldwide license of materials and know-how from the University of Michigan,
which owns the master donor strains from which our vaccine is derived; and (2)
an exclusive license of know-how and clinical trial data from the National
Institutes of Health, or NIH. Neither the University of Michigan nor the NIH has
been issued any patents covering the master donor strains. A third party may
gain access by some means to the University of Michigan master donor strains and
attempt to reproduce FluMist or develop another live virus influenza vaccine
that might be comparable to FluMist in terms of safety and effectiveness.

FAILURE TO RAISE ADDITIONAL CAPITAL COULD DELAY FLUMIST COMMERCIALIZATION AND
DELAY THE DEVELOPMENT OF A LIQUID FORMULATION OF FLUMIST AND OF OUR OTHER
POTENTIAL PRODUCTS.

     Our operations to date have consumed substantial and increasing amounts of
cash. As of June 30, 2000, we had an accumulated deficit of approximately $231.9
million. The negative cash flow from operations is expected to continue and to
accelerate in the foreseeable future. The commercialization of FluMist will
require a commitment of substantial funds for manufacturing, continued clinical
trial efforts and other commercialization activities. We also expect to spend a
substantial amount to develop a liquid formulation of FluMist. In addition, we
expect to continue funding the research, preclinical testing and clinical trials
necessary to develop our early-stage products. We expect our current capital
resources and financing commitments will enable us to maintain our current and
planned operations into 2001. We expect that we will need to raise additional
funds in the future. Our future capital requirements will depend upon many
factors, including:

     - product commercialization activities;

     - time and costs involved in obtaining regulatory approvals;

     - increasing manufacturing capacity for FluMist;

     - the progress of preclinical testing and clinical trials;

     - continued scientific progress in the research and development of our
       vaccine programs; and

     - the addition of other early-stage programs to our product pipeline.

If adequate funds are not available, the commercialization of FluMist may be
delayed, we may need to delay the development of a liquid formulation of
FluMist, and we will be required to delay, reduce the scope of, or eliminate one
or more of our research or development programs. If additional funds are raised
by issuing equity or convertible securities, percentage ownership in Aviron by
existing stockholders will be reduced.

IF WE ARE UNABLE TO ATTRACT AND RETAIN ADDITIONAL QUALIFIED PERSONNEL, OUR
ABILITY TO COMMERCIALIZE FLUMIST AND DEVELOP A LIQUID FORMULATION OF FLUMIST MAY
BE DELAYED.

     Attracting and retaining significant additional qualified personnel will be
critical to our success. To pursue the development and commercialization of
FluMist, we will be required to hire additional qualified personnel, especially
those with expertise in development, commercial-scale manufacturing, and quality
functions. Expansion in these areas is also expected to require the addition of
management personnel and the development of additional expertise by existing
management personnel. We face competition for qualified individuals from
numerous pharmaceutical, biopharmaceutical and biotechnology companies.



                                       6
<PAGE>   9

OTHER RISKS RELATED TO OUR COMPANY

SAFETY OF VACCINES CAN ONLY BE DETERMINED AFTER WIDESPREAD USE IN THE
POPULATION.

     A vaccine could be licensed by the FDA and still be associated with adverse
events which reduce or eliminate revenue. For example, in 1998 the FDA approved
the use of a vaccine to prevent infant diarrhea, but the product was
subsequently withdrawn from the market due to a possible link between a serious
bowel disorder and the vaccine. This adverse event occurred at a frequency that
was not detectable in a typical clinical development program. In addition there
are a number of theoretical risks related to live virus vaccines, including
changing back to the naturally-occurring, or wild-type, and re-combining to form
a new strain which may cause disease. Also, because of the way it works, a
weakened live virus could make an individual more susceptible to secondary
infection. In addition, a weakened live virus could cause disease resembling a
wild-type virus infection in people with an immune system that is not working
properly because of a pre-existing disease, HIV infection or drug treatment for
cancer or organ transplantation. The potential for adverse events after
introduction to the market is an issue for all vaccines, including FluMist.

OTHER THAN FLUMIST, OUR PRODUCT CANDIDATES ARE AT EARLY STAGES OF DEVELOPMENT,
AND IF WE ARE UNABLE TO SUCCESSFULLY DEVELOP AND COMMERCIALIZE PRODUCTS, WE WILL
NOT GENERATE REVENUES FROM THESE PRODUCTS.

     To date, none of our product candidates has been commercialized. Other than
FluMist, all of our product candidates are in early stages of development. We
face the risk of failure normally found in developing biotechnology products
based on new technologies. Successfully developing, manufacturing, introducing
and marketing our early-stage product candidates will require several years and
substantial additional capital. Moreover, we must demonstrate safety and
efficacy and gain regulatory approval for these products. We are aware of
several companies that are marketing or are in late-stage development of
products that would be competitive with our early-stage product candidates.

     In 1996, we completed construction of a pilot manufacturing facility for
our potential vaccine products other than FluMist. We currently do not have
facilities to manufacture any of our other potential products in commercial
quantities and have no experience with commercial manufacture of vaccine
products. We are alternatively considering the use of contract manufacturers for
the commercial production of our other potential products. We are aware of only
a limited number of manufacturers that we believe have the ability and capacity
to manufacture our other potential products in a timely manner.

WE MAY NOT RECEIVE PATENT PROTECTION FOR OUR POTENTIAL PRODUCTS AND
MANUFACTURING PROCESSES.

     Our success depends to a significant degree upon our ability to develop
proprietary products. Since patent applications in the United States are
maintained in secrecy until patents issue and since publication of discoveries
in the scientific or patent literature often lag behind actual discoveries, we
cannot be certain that we were the first to make the inventions covered by each
of our pending patent applications or that we were the first to file patent
applications for these inventions. The patent positions of biotechnology and
pharmaceutical companies can be highly uncertain and involve complex legal and
factual questions. Therefore, the breadth of claims allowed in biotechnology and
pharmaceutical patents, or their enforceability, cannot be predicted. We cannot
be sure that any of our owned or licensed patents or patent applications will
issue or, if issued, will not be invalidated or circumvented, or that the rights
granted by them will provide any protection or competitive advantages to us.

     The European Patent Office has informed us of its intention to deny claims
relating to methods and compositions of recombinant non-segmented
negative-strand RNA viruses contained in one of our granted European patents.
Although this decision will not affect our FluMist cold-adapted influenza
product, it may affect the European patent protection afforded our other vaccine
candidates, including recombinant RSV and recombinant PIV.

OUR PRODUCTS COULD INFRINGE THE INTELLECTUAL PROPERTY RIGHTS OF OTHERS, CAUSING
COSTLY LITIGATION AND THE LOSS OF SIGNIFICANT RIGHTS.

     Our success will also depend upon us not infringing patents issued to
others. A number of pharmaceutical companies, biotechnology companies,
universities and research institutions have filed patent applications or
received patents in the areas of our research and development programs. Some of
these patent applications or patents may limit the scope of claims issuing from
our patent applications, prevent certain claims from being issued, or conflict
in certain respects with claims made under our applications.

OUR BUSINESS EXPOSES US TO PRODUCT LIABILITY CLAIMS AND THE DEFENSE OR LOSS OF
ANY SUCH CLAIM COULD BE COSTLY.

     Our business exposes us to potential product liability risks that are
inherent in the testing, manufacturing and marketing of vaccines. We have
obtained clinical trial liability insurance for our clinical trials. We also
intend to seek product liability insurance in the future for products approved
for marketing. However, we cannot be sure that we will be able to acquire or
maintain insurance at a reasonable cost or in sufficient amounts to protect us
from liability risks. A successful product liability claim or a series of claims
brought against us could seriously harm our business. We intend to seek
inclusion of some of our products in the United States National Vaccine Injury
Compensation Program, a no-fault compensation program for claims against vaccine
manufacturers, which administers a trust funded by excise taxes on sales of a
number of recommended childhood vaccines. We cannot be sure that this government
program will continue or that our proposed vaccines will be included in the
program.

WE USE HAZARDOUS MATERIALS IN OUR BUSINESS AND AN ACCIDENT COULD BE COSTLY.

     Our business activities involve the controlled use of hazardous materials,
chemicals, various radioactive substances and viruses. Although we believe that
our safety procedures for handling and disposing of these materials comply with
state and federal regulations, the risk of accidental contamination or injury
from these materials cannot be completely eliminated. In the event of such an
accident, we could be held liable for any damages that result and any such
liability would seriously harm our business. In addition, we may incur
substantial costs to comply with



                                       7
<PAGE>   10

environmental regulations if we develop manufacturing capacity.

RISKS RELATED TO THIS OFFERING

OUR STOCK PRICE IS VOLATILE AND YOU MAY LOSE ALL OR A PART OF YOUR INVESTMENT.

     The market price of our common stock has fluctuated significantly to date.
As a result you may be unable to sell your shares of common stock at or above
the offering price. The market price of the common stock may fluctuate
significantly in response to the following factors, most of which are beyond our
control:

     - variations in our quarterly operating results;

     - changes in securities analysts' estimates of our financial performance;

     - changes in market valuations of similar companies;

     - announcements by us or our competitors of significant contracts,
       acquisitions, strategic partnerships, joint ventures or capital
       commitments;

     - additions or departures of key personnel; and

     - fluctuations in stock market price and volume, which are particularly
       common among securities of biopharmaceutical companies.

WE ARE AT RISK OF SECURITIES CLASS ACTION LITIGATION DUE TO OUR EXPECTED STOCK
PRICE VOLATILITY.

     In the past, securities class action litigation has often been brought
against a company following a decline in the market price of its securities.
This risk is especially relevant for us because biopharmaceutical companies have
experienced greater than average stock price volatility in recent years and, as
a result, have been subject to, on average, a greater number of securities class
action claims than companies in other industries. We may in the future be the
target of similar litigation. Securities litigation could result in substantial
costs and divert management's attention and resources, and could seriously harm
our business.

WE HAVE IMPLEMENTED ANTI-TAKEOVER PROVISIONS WHICH COULD DISCOURAGE OR PREVENT A
TAKEOVER, EVEN IF AN ACQUISITION COULD BE BENEFICIAL TO OUR STOCKHOLDERS.

     Provisions of our amended and restated certificate of incorporation and
bylaws, as well as provisions of Delaware law, could make it more difficult for
a third party to acquire us, even if doing so could be beneficial to our
stockholders. These provisions include:

     - establishment of a classified board of directors requiring that not all
       members of the board may be elected at one time;

     - prohibiting cumulative voting in the election of directors, which would
       otherwise allow less than a majority of stockholders to elect director
       candidates;

     - limitations on the ability of stockholders to call special meetings of
       stockholders;

     - prohibiting stockholder action by written consent, thereby requiring all
       stockholder actions to be taken at a meeting of our stockholders; and

     - establishing advance notice requirements for nominations for election to
       the board of directors or for proposing matters that can be acted upon by
       stockholders at stockholder meetings.

     In October 1997, our board of directors adopted a share purchase rights
plan, commonly referred to as a "poison pill." In addition, Section 203 of the
Delaware General Corporations Law and the terms of our stock option plans may
discourage, delay or prevent a change in control of our company.



                                       8
<PAGE>   11

                SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

     Some of the statements in the sections entitled "Summary," "Risk Factors,"
and elsewhere in this prospectus constitute forward-looking statements. These
statements involve known and unknown risks, uncertainties and other factors that
may cause our or our industry's results, levels of activity, or achievements to
be materially different from any future results, levels of activity or
achievements expressed or implied by such forward-looking statements. Such
factors include, among others, those listed under "Risk Factors" and elsewhere
in this prospectus.

     In some cases, you can identify forward-looking statements by terminology
such as "may," "will," "should," "intend," "expect," "plan," "anticipate,"
"believe," "estimate," "predict," "potential," or "continue," or the negative of
such terms or other comparable terminology.

     Although we believe that the expectations reflected in the forward-looking
statements are reasonable, we cannot guarantee future results, events, levels of
activity, performance or achievements. We do not assume responsibility for the
accuracy and completeness of the forward-looking statements. We do not intend to
update any of the forward-looking statements after the date of this prospectus
to conform such statements to actual results.

                                 USE OF PROCEEDS

     We will not receive any of the proceeds from the sale of shares of common
stock offered by the selling stockholders.



                                       9
<PAGE>   12

                              SELLING STOCKHOLDERS

    In a series of private placements, we sold to American Home Products
Corporation common stock and agreed to register the common stock for resale. We
issued to the other selling stockholders common stock upon the exercise of
warrants and issued additional warrants to purchase common stock both in
connection with the licensing of certain technology, and also agreed to register
the common stock and the shares of common stock issuable upon the exercise of
the warrants. The shares being registered represent approximately 4.7 percent of
our outstanding capitalization as of August 30, 2000.

    The following table sets forth information known to us with respect to
beneficial ownership of our common stock as of August 30, 2000 by each selling
stockholder. The following table assumes that the selling stockholders sell all
of the shares. We are unable to determine the exact number of shares that
actually will be sold.

    Beneficial ownership is determined in accordance with the rules of the SEC
and includes sole or shared voting or investment power with respect to shares
shown as beneficially owned. Percentage ownership is based on 21,933,008 shares
of common stock outstanding as of August 30, 2000. Unless otherwise indicated,
the address for each of the individuals listed in the table is c/o Aviron, 297
North Bernardo Avenue, Mountain View, California 94043.

<TABLE>
<CAPTION>
                                                           SHARES BENEFICIALLY        SHARES OFFERED        SHARES BENEFICIALLY
                                                            OWNED PRIOR TO THE           BY THIS            OWNED SUBSEQUENT TO
                                                                 OFFERING               PROSPECTUS              THE OFFERING
                                                         ------------------------     --------------     -----------------------
NAME AND ADDRESS OF SELLING STOCKHOLDER                   SHARES          PERCENT                         SHARES         PERCENT
                                                         --------         -------                        --------        -------
<S>                                                      <C>              <C>         <C>                <C>             <C>
American Home Products Corporation ..............         996,840          4.54%          996,840               0           *
 5 Giralda Farms, Madison, New Jersey 07940

Mount Sinai School of Medicine (1) ..............          50,642             *            27,309          23,333           *
 633 Third Avenue, New York, New York 10017

Mark Krystal ....................................           5,338             *             3,758           1,580           *

Jeffrey David Parvin (2) ........................           4,695             *             4,695               0           *

Michael Bergmann ................................           2,669             *             1,503           1,166           *

Thomas Muster ...................................           2,668             *             1,502           1,166           *

Reinhard Vlasak (3) .............................           2,001             *             1,126             875           *

Masayoshi Emami (4) .............................           1,502             *             1,502               0           *
</TABLE>

----------
* Less than 1% of the outstanding shares of common stock.

(1)  Includes 23,976 shares issuable upon exercise of warrants held by this
     selling stockholder.

(2)  Includes 2,610 shares issuable upon exercise of warrants held by this
     selling stockholder.

(3)  Includes 901 shares issuable upon exercise of warrants held by this selling
     stockholder.

(4)  Includes 1,202 shares issuable upon exercise of warrants held by this
     selling stockholder.

    We are registering the shares for resale by the selling stockholders in
accordance with registration rights granted to the selling stockholders. We will
pay the registration and filing fees, printing expenses, listing fees, blue sky
fees, if any, and fees and disbursements of our counsel and the selling security
holders' counsel in connection with this offering, but the selling stockholders
will pay any underwriting discounts, selling commissions and similar expenses
relating to the sale of the shares. In addition, we have agreed to indemnify the
selling stockholders against certain liabilities, including liabilities under
the Securities Act, in connection with this offering. The selling stockholders
have agreed to indemnify us and our directors and officers, as well as any
person that controls us, against certain liabilities, including liabilities
under the Securities Act. Insofar as indemnification for liabilities under the
Securities Act may be permitted to our directors or officers, or persons that
control us, we have been informed that in the opinion of the SEC such
indemnification is against public policy as expressed in the Securities Act and
is therefore unenforceable.



                                       10
<PAGE>   13

                              PLAN OF DISTRIBUTION

    The selling stockholders, or, subject to applicable law, their pledgees,
donees, distributees, transferees or other successors in interest, may sell
shares from time to time in public transactions, on or off the Nasdaq National
Market, or private transactions, at prevailing market prices or at privately
negotiated prices, including but not limited to, one or any combination of the
following types of transactions:

      o     ordinary brokers' transactions;

      o     transactions involving cross or block trades or otherwise on the
            Nasdaq National Market;

      o     purchases by brokers, dealers or underwriters as principal and
            resale by these purchasers for their own accounts pursuant to this
            prospectus;

      o     "at the market," to or through market makers, or into an existing
            market for our common stock;

      o     in other ways not involving market makers or established trading
            markets, including direct sales to purchasers or sales effected
            through agents;

      o     through transactions in options, swaps or other derivatives (whether
            exchange-listed or otherwise);

      o     in privately negotiated transactions; or

      o     to cover short sales.

    In effecting sales, brokers or dealers engaged by the selling stockholders
may arrange for other brokers or dealers to participate in the resales. The
selling stockholders may enter into hedging transactions with broker-dealers,
and in connection with those transactions, broker-dealers may engage in short
sales of the shares. The selling stockholders also may sell shares short and
deliver the shares to close out such short positions. The selling stockholders
also may enter into option or other transactions with broker-dealers that
require the delivery to the broker-dealer of the shares, which the broker-dealer
may resell pursuant to this prospectus. The selling stockholders also may pledge
the shares to a broker or dealer. Upon a default, the broker or dealer may
effect sales of the pledged shares pursuant to this prospectus.

    Brokers, dealers or agents may receive compensation in the form of
commissions, discounts or concessions from selling stockholders in amounts to be
negotiated in connection with the sale. The selling stockholders and any
participating brokers or dealers may be deemed to be "underwriters" within the
meaning of the Securities Act in connection with such sales. In such event, any
commission, discount or concession these "underwriters" receive may be deemed to
be underwriting compensation.

    To the extent required, the following information will be set forth in a
supplement to this prospectus:

      o     information as to whether underwriters who the selling stockholders
            may select, or any other broker-dealer, is acting as principal or
            agent for the selling stockholders;

      o     the compensation to be received by underwriters that the selling
            stockholders may select or by any broker-dealer acting as principal
            or agent for the selling stockholder; and

      o     the compensation to be paid to other broker-dealers, in the event
            the compensation of such other broker-dealers is in excess of usual
            and customary commissions.

    Any dealer or broker participating in any distribution of the shares may be
required to deliver a copy of this prospectus, including a prospectus
supplement, if any, to any person who purchases any of the shares from or
through this dealer or broker.

    We have advised the selling stockholders that they are required to comply
with Regulation M promulgated under the Securities Exchange Act during such time
as they may be engaged in a distribution of the shares. With certain exceptions,
Regulation M precludes any selling stockholders, any affiliated purchasers and
any broker-dealer or other person who participates in such distribution from
bidding for or purchasing, or attempting to induce any person to bid for or
purchase any security that is the subject of the distribution until the entire
distribution is complete. Regulation M also prohibits any bids or purchases made
in order to stabilize the price of a security in connection with the
distribution of that security. All of the foregoing may affect the marketability
of the common stock.

    We will not receive any of the proceeds from the selling stockholders' sale
of our common stock.

    This registration statement will remain effective until the earlier of (a)
the date when all of the shares registered by this registration statement have
been distributed to the public, or (b) the date the shares of common stock are
eligible for sale in their entirety under Rule 144. In the event that any shares
remain unsold at the end of such period. We may file a post-effective amendment
to the registration statement for the purpose of deregistering the shares
registered by this prospectus.



                                       11
<PAGE>   14

                                  LEGAL MATTERS

    For the purpose of this offering, Cooley Godward LLP, Palo Alto, California
is giving an opinion of the validity of the issuance of the common stock offered
in this prospectus.

                                     EXPERTS

    Ernst & Young LLP, independent auditors have audited our financial
statements included in our Annual Report on Form 10-K/A for the year ended
December 31, 1999, as set forth in their report, which is incorporated by
reference in this prospectus and elsewhere in the registration statement. Our
financial statements are incorporated by reference in reliance on Ernst & Young
LLP's report, given on their authority as experts in accounting and auditing.



                                       12
<PAGE>   15

                                     PART II

                     INFORMATION NOT REQUIRED IN PROSPECTUS

ITEM 14. OTHER EXPENSES OF ISSUANCE AND DISTRIBUTION

<TABLE>
<S>                                                                    <C>
Securities and Exchange Commission Registration Fee ...........        $10,861
Legal Fees and Expenses .......................................         25,000
Accountants' Fees and Expenses ................................         15,000
Miscellaneous .................................................          4,139

        Total .................................................        $55,000
                                                                       =======
</TABLE>

The foregoing items, except for the Securities and Exchange Commission
Registration Fee are estimated.

ITEM 15. INDEMNIFICATION OF DIRECTORS AND OFFICERS

    Under Section 145 of the Delaware General Corporation Law, Aviron has broad
powers to indemnify its directors and officers against liabilities they may
incur in such capacities, including liabilities under the Securities Act of
1933.

    Aviron's certificate of incorporation and by-laws include provisions to (1)
eliminate the personal liability of its directors for monetary damages resulting
from breaches of their fiduciary duty to the extent permitted by Section
102(b)(7) of the General Corporation Law of Delaware and (2) require Aviron to
indemnify its directors and officers to the fullest extent permitted by Section
145 of the Delaware Law, including circumstances in which indemnification is
otherwise discretionary. Pursuant to Section 145 of the Delaware Law, a
corporation generally has the power to indemnify its present and former
directors, officers, employees and agents against expenses incurred by them in
connection with any suit to which they are, or are threatened to be made, a
party by reason of their serving in such positions so long as they acted in good
faith and in a manner they reasonably believed to be in, or not opposed to, the
best interest of the corporation, and with respect to any criminal action, they
had no reasonable cause to believe their conduct was unlawful. Aviron believes
that these provisions are necessary to attract and retain qualified persons as
directors and officers. These provisions do not eliminate the directors' duty of
care, and, in appropriate circumstances, equitable remedies such as injunctive
or other forms of non-monetary relief will remain available under Delaware law.
In addition, each director will continue to be subject to liability for breach
of the directors' duty of loyalty to Aviron, for acts or omissions not in good
faith or involving intentional misconduct, for knowing violations of law, for
acts or omissions that the director believes to be contrary to the best
interests of Aviron or its stockholders, for any transaction from which the
director derived an improper personal benefit, for acts or omissions involving a
reckless disregard for the directors' duty to Aviron or its stockholders when
the director was aware or should have been aware of a risk of serious injury to
Aviron or its stockholders, for acts or omissions that constitute an unexcused
pattern of inattention that amounts to an abdication of the director's duty to
Aviron or its stockholders, for improper transactions between the director and
Aviron and for improper distributions to stockholders and loans to directors and
officers. The provision also does not affect a director's responsibilities under
any other law, such as the federal securities law or state or federal
environmental laws.

    Aviron has entered into indemnity agreements with each of its directors and
executive officers that require Aviron to indemnify such persons against
expenses, judgments, fines, settlements and other amounts incurred (including
expenses of a derivative action) in connection with any proceeding, whether
actual or threatened, to which any such person may be made a party by reason of
the fact that such person is or was a director or an executive officer of Aviron
or any of its affiliated enterprises, provided such person acted in good faith
and in a manner such persons reasonably believed to be in, or not opposed to,
the best interests of Aviron and, with respect to any criminal proceeding, has
no reasonable cause to believe his conduct was unlawful. The indemnification
agreements also set forth procedures that will apply in the event of a claim for
indemnification thereunder.

    At present, there is no pending litigation or proceeding involving a
director or officer of Aviron as to which indemnification is being sought.

    Aviron has an insurance policy covering the officers and directors of Aviron
with respect to certain liabilities, including liabilities arising under the
Securities Act or otherwise.

ITEM 16. EXHIBITS

<TABLE>
<CAPTION>
EXHIBIT NO.    DESCRIPTION OF DOCUMENT
-----------    -----------------------
<S>            <C>
 4.2           Specimen Stock Certificate. (1)
 4.8           Investors Rights Agreement, dated July 18, 1995, among the
               Company and the investors named therein.  (1)
 4.11          Common Stock Purchase Agreement, dated as of December 16, 1999,
               between the Company and American Home Products Corporation.  (2)
 4.12          Common Stock Purchase Agreement, dated as of December 30, 1999,
               between the Company and American Home Products Corporation.  (2)
 4.13          Common Stock Purchase Agreement, dated as of February 3, 2000,
               between the Company and American Home Products Corporation.  (2)
 4.15          Common Stock Purchase Agreement, dated as of April 5, 2000,
               between the Company and American Home Products Corporation.  (3)
 5.1           Opinion of Cooley Godward LLP.
23.1           Consent of Ernst & Young LLP, Independent Auditors.
23.2           Consent of Cooley Godward LLP. Reference is made to Exhibit 5.1.
24.1           Power of Attorney.  See signature page.
</TABLE>
---------
(1) Incorporated by reference to the correspondingly numbered exhibit to our
    Registration Statement on Form S-1, File No. 333-05209, filed June 5, 1996,
    as amended.

(2) Incorporated by reference to the correspondingly numbered exhibit to our
    Annual Report on Form 10-K for the year ended December 31, 1999, File No.
    0-20815, filed March 8, 2000.

(3) Incorporated by reference to the correspondingly numbered exhibit to our
    Quarterly Report on Form 10-Q for the quarter ended March 31, 2000, File No.
    0-20815, filed May 15, 2000.

                                      II-1


<PAGE>   16

ITEM 17. UNDERTAKINGS

    Insofar as indemnification for liabilities arising under the Securities Act
of 1933, may be permitted to directors, officers, and controlling persons of the
Registrant pursuant to the provisions described in Item 15 or otherwise, the
Registrant has been advised that in the opinion of the Securities and Exchange
Commission, such indemnification is against public policy as expressed in the
Securities Act of 1933 and is, therefore, unenforceable. In the event that a
claim for indemnification against such liabilities (other than the payment by
the Registrant of expenses incurred or paid by a director, officer, or
controlling person of the Registrant in the successful defense of any action
suit, or proceeding) is asserted by such director, officer, or controlling
person in connection with the securities being registered, the Registrant will,
unless in the opinion of its counsel the matter has been settled by controlling
precedent, submit to a court of appropriate jurisdiction the question whether
such indemnification by it is against public policy as expressed in the
Securities Act of 1933 and will be governed by the final adjudication of such
issue.

The undersigned registrant hereby undertakes:

    (1) To file, during any period in which offers or sales are being made
    pursuant to this registration statement: (i) To include any prospectus
    required by Section 10(a)(3) of the Securities Act of 1933; (ii) To reflect
    in the prospectus any facts or events arising after the effective date of
    the registration statement (or the most recent post-effective amendment
    thereof) which, individually or in the aggregate, represent a fundamental
    change in the information set forth in the registration statement.
    Notwithstanding the foregoing, any increase or decrease in volume of
    securities offered (if the total dollar value of securities offered would
    not exceed that which was registered) and any deviation from the low or high
    end of the estimated maximum offering range may be reflected in the form of
    prospectus filed with the Commission pursuant to Rule 424(b) if, in the
    aggregate, the changes in volume and price represent no more than a 20
    percent change in the maximum aggregate offering price set forth in the
    "Calculation of Registration Fee" table in the effective registration
    statement; (iii) To include any material information with respect to the
    distribution not previously disclosed in the registration statement or any
    material change to such information in the registration statement;

    (2) That, for the purpose of determining any liability under the Securities
    Act of 1933, each such post-effective amendment shall be deemed to be a new
    registration statement relating to the securities offered therein, and the
    offering of such securities at that time shall be deemed to be the initial
    bona fide offering thereof; and

    (3) To remove from registration by means of a post-effective amendment any
    of the securities being registered which remain unsold at the termination of
    the offering.

    The undersigned Registrant hereby undertakes that, for the purposes of
determining any liability under the Securities Act of 1933, each filing of the
Registrant's annual report pursuant to Section 13(a) of Section 15(d) of the
Securities Exchange Act of 1934 that is incorporated by reference in the
registration statement shall be deemed to be a new registration statement
relating to the securities offered therein, and the offering of such securities
at that time shall be deemed to be the initial bona fide offering thereof.

The undersigned Registrant undertakes that; (1) for purpose of determining any
liability under the Securities Act of 1933, the information omitted from the
form of prospectus filed as part of the registration statement in reliance upon
Rule 430A and contained in the form of prospectus filed by the Registrant
pursuant to Rule 424(b) (1) or (4) or 497(h) under the Securities Act shall be
deemed to be part of the registration statement as of the time it was declared
effective; and (2) for the purpose of determining any liability under the
Securities Act of 1933, each post-effective amendment that contains a form of
prospectus shall be deemed to be a new registration statement relating to the
securities offered therein, and the offering of such securities at that time
shall be deemed to be the initial bona fide offering thereof.



                                      II-2
<PAGE>   17

                                   SIGNATURES

        Pursuant to the requirements of the Securities Act of 1933, the
Registrant certifies that it has reasonable grounds to believe that it meets all
of the requirements for filing on Form S-3 and has duly caused this Registration
Statement on Form S-3 to be signed on its behalf by the undersigned, thereunto
duly authorized, in the City of Mountain View, County of Santa Clara, State of
California, on September 1, 2000.

                                       AVIRON


                                       By:     /s/ C. Boyd Clarke
                                          --------------------------------------
                                           C. Boyd Clarke
                                           President and Chief Executive Officer

                                POWER OF ATTORNEY

    KNOW ALL PERSON BY THESE PRESENTS, that each person whose signature appears
below constitutes and appoints C. Boyd Clarke and Fred Kurland, his or her true
and lawful agent, proxy and attorney-in-fact, each acting alone, with full power
of substitution and resubstitution, for him or her and in his or her name, place
and stead, in any and in any and all capacities, to (1) act on, sign and file
with the Securities and Exchange Commission any and all amendments (including
post-effective amendments) to this registration statement together with all
schedules and exhibits thereto and any subsequent registration statement filed
pursuant to Rule 462(b) under the Securities Act of 1933, as amended, together
with all schedules and exhibits thereto, (2) act on, sign and file such
certificates, instruments, agreements and other documents as may be necessary or
appropriate in connection therewith, (3) act on and file any supplement to any
prospectus included in this registration statement or any such amendment or any
subsequent registration statement filed pursuant to Rule 462(b) under the
Securities Act of 1933, as amended, and (4) take any and all actions which may
be necessary or appropriate to be done, as fully for all intents and purposes as
he or she might or could do in person, hereby approving, ratifying and
confirming all that such agent, proxy and attorney-in-fact or any of his
substitutes may lawfully do or cause to be done by virtue thereof.

        PURSUANT TO THE REQUIREMENTS OF THE SECURITIES ACT OF 1933, AS AMENDED,
THIS REGISTRATION STATEMENT ON FORM S-3 HAS BEEN SIGNED BELOW BY THE FOLLOWING
PERSONS IN THE CAPACITIES AND ON THE DATES INDICATED.

<TABLE>
<CAPTION>
                  SIGNATURE                                          TITLE                                 DATE
                  ---------                                          -----                                 ----
<S>                                              <C>                                                 <C>


             /s/ C. Boyd Clarke                  President, Chief Executive Officer and Director     September 1, 2000
---------------------------------------------             (Principal Executive Officer)
               C. Boyd Clarke


              /s/ Fred Kurland                  Senior Vice President and Chief Financial Officer   September 1, 2000
---------------------------------------------     (Principal Financial and Accounting Officer)
                Fred Kurland


         /s/ J. Leighton Read, M.D.                       Chairman of the Board                     September 1, 2000
---------------------------------------------
           J. Leighton Read, M.D.


                                                                Director
---------------------------------------------
        R. Gordon Douglas, Jr., M.D.


         /s/ Dennis M. Fenton, Ph.D.                            Director                            September 1, 2000
---------------------------------------------
           Dennis M. Fenton, Ph.D.


        /s/ Wayne T. Hockmeyer, Ph.D.                           Director                            September 1, 2000
---------------------------------------------
          Wayne T. Hockmeyer, Ph.D.


          /s/ Paul H. Klingenstein                              Director                            September 1, 2000
---------------------------------------------
            Paul H. Klingenstein


            /s/ Alan C. Mendelson                               Director                            September 1, 2000
---------------------------------------------
              Alan C. Mendelson


         /s/ Bernard Roizman, Sc.D.                             Director                            September 1, 2000
---------------------------------------------
           Bernard Roizman, Sc.D.
</TABLE>



                                      II-3
<PAGE>   18

                                INDEX TO EXHIBITS

<TABLE>
<CAPTION>
EXHIBIT NO.    DESCRIPTION OF DOCUMENT
-----------    -----------------------
<S>            <C>
 4.2           Specimen Stock Certificate. (1)
 4.8           Investors Rights Agreement, dated July 18, 1995, among the
               Company and the investors named therein.  (1)
 4.11          Common Stock Purchase Agreement, dated as of December 16, 1999,
               between the Company and American Home Products Corporation.  (2)
 4.12          Common Stock Purchase Agreement, dated as of December 30, 1999,
               between the Company and American Home Products Corporation.  (2)
 4.13          Common Stock Purchase Agreement, dated as of February 3, 2000,
               between the Company and American Home Products Corporation.  (2)
 4.15          Common Stock Purchase Agreement, dated as of April 5, 2000,
               between the Company and American Home Products Corporation.  (3)
 5.1           Opinion of Cooley Godward LLP.
23.1           Consent of Ernst & Young LLP, Independent Auditors.
23.2           Consent of Cooley Godward LLP. Reference is made to Exhibit 5.1.
24.1           Power of Attorney.  See signature page.
</TABLE>
---------
(1) Incorporated by reference to the correspondingly numbered exhibit to our
    Registration Statement on Form S-1, File No. 333-05209, filed June 5, 1996,
    as amended.

(2) Incorporated by reference to the correspondingly numbered exhibit to our
    Annual Report on Form 10-K for the year ended December 31, 1999, File No.
    0-20815, filed March 8, 2000.

(3) Incorporated by reference to the correspondingly numbered exhibit to our
    Quarterly Report on Form 10-Q for the quarter ended March 31, 2000, File No.
    0-20815, filed May 15, 2000.




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