<PAGE>
Rule 497(c)
File No. 333-05227
SUPPLEMENT DATED SEPTEMBER 13, 1999
TO
PROFILE DATED MAY 1, 1999
AND
PROSPECTUS DATED MAY 1, 1999
FOR
MFS REGATTA CLASSIC
VARIABLE AND FIXED ANNUITY
ISSUED BY SUN LIFE ASSURANCE COMPANY OF CANADA (U.S.)
Effective November 1, 1999, with the addition of a new Series -- the
Strategic Growth Series -- to the MFS/Sun Life Series Trust (the "Series Fund"),
you may allocate your money among 26 variable investment options available under
the MFS Regatta Classic Variable and Fixed Annuity. Market conditions will
determine the value of an investment in the Strategic Growth Series and any
other Series of the Series Fund. The Strategic Growth Series and the other
Series of the Series Fund are described in the Series Fund prospectus, as
supplemented.
As a result of the addition of the Strategic Growth Series, the Profile
dated May 1, 1999 (the "Profile") and the Prospectus dated May 1, 1999 (the
Prospectus") are hereby amended and supplemented as follows:
1. The third paragraph of Section 1, The MFS Regatta Classic Annuity, of
the Profile and the second paragraph on the cover page of the Prospectus are
each amended by deleting the first sentence in its entirety and replacing it
with the following:
"You may choose among 26 variable investment options and a range of fixed
options."
2. The list of the available investment options appearing in Section 4,
Allocation Options, of the Profile and on the cover page of the Prospectus is
hereby supplemented by the addition of the Strategic Growth Series.
3. The summary expense chart appearing in Section 5, Expenses, of the
Profile is hereby supplemented as follows:
<TABLE>
<CAPTION>
EXAMPLES:
TOTAL ANNUAL TOTAL ANNUAL TOTAL TOTAL EXPENSES
INSURANCE SERIES ANNUAL AT END
SUB-ACCOUNT CHARGES EXPENSES EXPENSES 1 YEAR 10 YEARS
- ----------- ------- -------- -------- ------ --------
<S> <C> <C> <C> <C> <C>
Strategic Growth Series 1.25% 1.03% 2.28% $33 $262
(1.15% + 0.10%)
</TABLE>
4. The "Series Fund Annual Expenses" table and the footnotes thereto
appearing on page 5 of the Prospectus are hereby supplemented as follows:
<TABLE>
<CAPTION>
OTHER TOTAL FUND
MANAGEMENT EXPENSES (2) EXPENSES
FEES (AFTER REIMBURSEMENT) (AFTER REIMBURSEMENT)
-------------- ----------------------- -----------------------
<S> <C> <C> <C>
Strategic Growth Series (4) 0.75% 0.28% 1.03%
</TABLE>
<PAGE>
(4) MFS has contractually agreed to bear the Series' expenses such
that "Other Expenses" will not exceed 0.25% annually. This
contractual arrangement will remain in effect until at least
May 1, 2000, absent an earlier modification by the Series
Fund's Board of Trustees.
Additionally, the Series has an expenses offset arrangement
which reduces its custodian fee based upon the amount of cash
maintained by the Series with its custodian and dividend
disbursing agent. The Series may enter into other similar
arrangements and directed brokerage arrangements, which would
also have the effect of reducing the Series' expenses. The
Series' expenses do not take into account these expense
reductions, and therefore do not represent the actual expenses
of the Series. If these expense reductions had been taken into
account, "Total Fund Expenses" for the Series would be 1.00%.
4. The "Examples" presented on page 6 of the Prospectus are supplemented
as follows:
If you surrender your Contract at the end of the applicable time
period, you would pay the following expenses on a $1,000 investment, assuming a
5% annual return:
<TABLE>
<CAPTION>
1 YEAR 3 YEARS 5 YEARS 10 YEARS
------ ------- ------- --------
<S> <C> <C> <C> <C>
Strategic Growth Series $33 $71 $122 $262
</TABLE>
If you do NOT surrender your Contract, or if you annuitize at the
end of the applicable time period, you would pay the following expenses on a
$1,000 investment, assuming a 5% annual return:
<TABLE>
<CAPTION>
1 YEAR 3 YEARS 5 YEARS 10 YEARS
------ ------- ------- --------
<S> <C> <C> <C> <C>
Strategic Growth Series $23 $71 $122 $262
</TABLE>
5. The "Variable Account Options: The MFS/Sun Life Series Trust" section
beginning on page 8 of the Prospectus, is supplemented as follows:
"STRATEGIC GROWTH SERIES will seek capital appreciation."
THIS SUPPLEMENT IS NOT VALID UNLESS ACCOMPANIED OR PRECEDED BY THE CURRENT
PROSPECTUS OF MFS REGATTA CLASSIC VARIABLE AND FIXED ANNUITY, DATED MAY 1,
1999, AND THE CURRENT PROSPECTUS OF THE MFS/SUN LIFE SERIES TRUST. THIS
SUPPLEMENT AND THE PROSPECTUSES SHOULD BE READ AND RETAINED FOR FUTURE
REFERENCE.
CLASSICSUPP-1 9/99
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