<PAGE>   1

                                                                   EXHIBIT 10.02

                               AMENDMENT AGREEMENT

         This Amendment Agreement (the "Amendment Agreement") is entered into as
of this 2nd day of November, 1998 by and between:

         1. PASTEUR MERIEUX Serums & Vaccins S.A., a societe anonyme existing
and organized under the laws of France, registered under number RCS LYON B 349
505 370, whose registered head office is located at 58, avenue Leclerc, 69007
Lyon, France (hereinafter referred to as "PMC");

and

         2. ORAVAX, Inc., a corporation existing and organized under the laws of
the State of Delaware, having its principal place of business at 38 Sidney
Street, Cambridge, Massachusetts, United States of America (hereinafter referred
to as "OraVax").

         Capitalized terms used but not defined herein shall have the same
meanings assigned to them in the Master Agreement dated March 31, 1995 (the
"Master Agreement").

                                   WITNESSETH

         WHEREAS, OraVax and PMC have entered into the Master Agreement with
respect to the development of products for the treatment and/or prevention of
Helicobacter pylori infections; and

         WHEREAS, pursuant to the Master Agreement, OraVax directly or
indirectly holds a 49.9% ownership interest in the U.S. Partnership and a 50.1%
ownership interest in the SNC; and

         WHEREAS, OraVax and PMC have entered into a Facility Agreement dated as
of the date hereof (the "Facility Agreement") pursuant to which PMC has granted
OraVax a loan in the amount of US$3,000,000 (the "Loan"); and

         WHEREAS, in connection with entering into the Facility Agreement, the
parties desire to amend certain terms of the Master Agreement;

         NOW, THEREFORE, in consideration of the mutual promises, conditions,
covenants and undertakings hereinafter set forth, the parties hereto, intending
to be legally bound, hereby agree as follows:

         1. Section 11.3 of the Master Agreement is hereby deleted and replaced
in its entirety with the following:
<PAGE>   2
         "11.3 Marketing Committee

         (a) The marketing activities of each of the Partnerships shall be
managed by a Marketing Committee comprised of a maximum of three (3)
representatives from each Party (the "Marketing Committee"). The purpose of the
Marketing Committees shall be to (a) consider and propose to their respective
Executive Committees a marketing plan, strategy and budget(s) for marketing of
Target Products (the "Marketing Plan"), (b) select and make recommendations to
their respective Executive Committees with respect to trademark(s) to be used in
connection with Target Products (in each case, based on the principle that there
shall be only one trademark for each Target Product on a worldwide basis unless
otherwise imposed by legal constraints) and (c) monitor prosecution of selected
trademark(s) and administrative expenses. PMC shall cast two votes on each of
the Marketing Committees and OraVax shall cast one vote (with two votes being
sufficient to direct all decisions of the Marketing Committee) on each of the
Marketing Committees and the chair of each Marketing Committee shall rotate
annually, and in any given year shall be occupied by a representative of the
Party not chairing the Executive Committees (with one Party chairing both
Marketing Committees in a single year). The Marketing Committees shall conduct
their respective proceedings in accordance with rules to be adopted by each
Committee.

         (b) The Marketing Committees shall each form a sub-committee, the
"Joint Medical Legal Review Board," which in each case shall be comprised of an
equal number of representatives of each Party, subject to Section 11.4 hereof.
All marketing and promotional materials proposed for use in connection with
Target Products shall be submitted for medical and legal review to this Board.
In the event that such Board cannot reach agreement, or either Party objects to
a ruling of the Board as to the acceptability of any marketing or promotional
material, such marketing or promotional piece shall not be used."

         2. Section 11.4 of the Master Agreement is hereby deleted and replaced
in its entirety with the following:


                                       2
<PAGE>   3
         "11.4 Change of Control and Reorganization of Committees

         In the event that (i) PMC's percentage of ownership interest in either
the U.S. Partnership or the SNC shall be increased above the percentage of
ownership interest held by PMC on the date hereof due to a transfer, sale,
assignment, pledge (other than a pledge related to the Loan) or other
disposition of Oravax' interest in the U.S. Partnership or the SNC (and not due
to a failure of Oravax to make Capital Contributions) or (ii) a Change of
Control of OraVax (as set forth in Section 15.2 of the Master Agreement, other
than a Change of Control involving Peptide Therapeutics, Limited), then the
Executive Committees, Marketing Committees and Program Committees shall be
reorganized as follows: PMC shall thereafter cast two votes on each such
committee, while OraVax shall cast but a single vote, and two votes shall
suffice to direct all decisions of the committee. In addition, a representative
of PMC shall at all times preside over the deliberations of the committees and
PMC may elect at any time by notice to OraVax either (1) to reduce the
representation of OraVax on each such committee by one member or (2) to increase
its own representation on such committees by one member, and in all such cases,
PMC shall have control of the decisions of each committee. Notwithstanding the
foregoing, in respect of all matters that relate to or could affect the
marketing of Target Products, PMC shall at all times cast two votes on any
Committee before which such matter is presented for a vote, including, without
limitation, the Executive Committee, the Programming Committee and the Marketing
Committee, and OraVax shall cast one vote (and two votes shall suffice to direct
the decision of such Committees). OraVax hereby authorizes PMC, or should PMC so
elect, PMC's Affiliates, to act as the principal marketing entity for any Target
Products."

         3. The parties hereto hereby agree that in the event OraVax repays the
Loan in full on or before June 30, 1999, the amendment set forth in Section 2
hereof shall no longer be of any force and effect and Section 11.4 of the Master
Agreement as previously in effect shall be restored.

         4. Except as expressly amended hereby, the Master Agreement and all
rights and obligations of the parties thereunder, shall remain in full force and
effect. This Amendment Agreement shall not be deemed to be a consent to any
waiver or modification of any other terms or provisions of the Master Agreement.


                                       3
<PAGE>   4
         IN WITNESS WHEREOF, this Amendment Agreement has been executed by each
of the parties on the date first above written.

PASTEUR MERIEUX Serums & Vaccins S.A.



By:  /s/ Herve Tainturier
     -------------------------------
Name:    Herve Tainturier
Title:   Senior Vice-President and General Counsel




By:  
Name:
Title:


ORAVAX, INC.


By:  /s/ Brigid A. Makes
     -------------------------------
Name:    Brigid A. Makes
Title:   Vice President, Finance



By:  /s/ Robert J. Gerety
     -------------------------------
Name:    Robert J. Gerety
Title:   Vice President, Development and Regulatory Affairs

<PAGE>   5

                                 FACILITY LETTER

                                          November 2, 1998

OraVax JVM, Inc.
38 Sidney Street
Cambridge, MA 02139

Re:   OraVax JVM, Inc. - Committed Credit Facility

Ladies and Gentlemen:

     The undersigned, Connaught Laboratories, Inc., a Delaware corporation (the
"Lender") is pleased to provide a secured committed credit facility (the
"Facility") to OraVax JVM, Inc., a Delaware corporation (the "Borrower") and a
wholly-owned subsidiary of OraVax, Inc., a Delaware corporation ("Parent"), in
an amount not to exceed U.S. $3,000,000.

     The Lender's commitment to extend the Facility, which shall be deemed
effective as of the Effective Date (as defined below), is specifically subject
to the terms and conditions as stated herein (the "Agreement"). This Agreement,
together with the Note (as defined below), the Pledge Agreement (as defined
below) and any and all other agreements, instruments and documents related to
any of the foregoing, are collectively referred to herein as the "Facility
Documents".

     1. FACILITIES AND EXTENSIONS OF CREDIT. The Facility will be in the maximum
principal amount of U.S. $3,000,000 (the "Committed Amount"). The Facility will
be a term loan facility and will be available in a single advance only (the
"Loan") and will be available to the Borrower, subject to the applicable
provisions of this Agreement, for the term specified in the following paragraph,
provided that once borrowed and repaid, amounts may not be reborrowed.

     The Loan will be payable, including any interest accrued up to such date,
on the earlier to occur of (i) the dates provided in subclause (b) of the next
following sentence setting out the repayment schedule for the Loan or (ii) the
date on which such Facility is terminated in accordance with the provisions
hereof (such earlier date, the "Maturity Date"). Unless otherwise accelerated
pursuant to the terms hereof, the Loan shall be repaid by the Borrower according
to the following schedule: (a) on January 31, 1999, the Borrower shall repay the
original principal of the loan in an amount equal to $2,000,000 and (b) on June
30, 1999, the Borrower shall repay the entire remaining outstanding principal
balance of the Loan in full, and, in each case such repayment shall include
interest accrued up to the date of such repayment on the amount being repaid on
such date.


                                       1


<PAGE>   6


     When the Borrower desires to utilize the Facility, a duly authorized
officer or representative of the Borrower shall advise the Lender in writing or
by telephone confirmed in writing. Once all of the conditions precedent set
forth in Section 6 have been satisfied in the Lender's sole discretion, the
Lender is authorized to credit to the specified account of the Borrower the Loan
as requested by the Borrower (subject to the limitation of the aggregate
principal amount as above stated).

     2. INTEREST AND MATURITY DATES OF LOANS. The Loan shall accrue interest
daily at the rate (the "Interest Rate") of five and 42 one hundredths of one
percent (5.42%) per annum on the principal amount of the Loan outstanding from
time to time hereunder from and including the date the Loan is advanced to, but
excluding the date the Loan is paid in full. Principal and accrued interest will
be paid as provided in Section 1 above (whether at the stated maturity or upon
earlier acceleration or otherwise) in immediately available funds and calculated
on the basis of the actual calendar days elapsed and a 365 day year.

     Any amounts that have become due and payable in accordance with this
Agreement, any Facility Document or otherwise (whether at stated maturity, by
acceleration or otherwise) and remain unpaid by the Borrower shall accrue
interest thereafter until payment in full of such amounts (both before and after
judgment) at an interest rate per annum equal to 2% above the Interest Rate (the
"Default Rate"), and such interest shall be calculated on the basis of the
actual calendar days elapsed in a 365 day year and shall be payable upon the
Lender's demand therefor. Notwithstanding any provision of this Agreement or any
Facility Document to the contrary, the interest payable with respect to the Loan
shall in no event exceed the maximum amount of interest permitted from time to
time by applicable law.

     3. NOTE. The Loan shall be evidenced by a promissory note (the "Note") in
the form of Exhibit A hereto. The Borrower hereby expressly authorizes the
Lender to record from time to time on the schedule attached to each relevant
Note the date and amount of the Loan, the Interest Rate, and the date and amount
of each payment or prepayment of principal thereon. All such notations shall
constitute prima facie evidence of the accuracy of the information so recorded
and shall be conclusive and binding upon the Borrower in the absence of manifest
error. Any failure to make any such notation, however, shall not limit or
otherwise affect the obligations of the Borrower in respect of the Loan or under
any Facility Document.

     4. PAYMENTS. All borrowings, payments and repayments shall be made upon a
day on which the Lender is open for business. If any payment of principal or
interest in respect of the Loan or any other amount due in respect of the
Facility or the Facility Documents becomes due on a day that is not a Business
Day, such payment shall be made on the next succeeding Business Day, and such
extension of time shall be included in computing interest in connection with
such payment.

     All payments to the Lender hereunder shall be made to such account as the
Lender shall direct in lawful money of the United States of America and in
immediately available funds.


                                       2


<PAGE>   7


     5. PREPAYMENTS. The Loan may be prepaid, in whole or in part, prior to the
stated maturity thereof, except as otherwise provided herein.

     6. CONDITIONS PRECEDENT TO THE LOAN. Prior to making the Loan to or for the
account of the Borrower hereunder, the Lender shall have received each of the
following in form and substance satisfactory to the Lender:

     (a)  executed originals of each of the Facility Documents, including,
          without limitation, this Agreement, the Note, the Pledge Agreement,
          together with all certificates evidencing the Collateral (as defined
          in the Pledge Agreement) duly indorsed in blank or to the order of the
          Lender and the UCC-1 financing statement referred to in Section 4.2 of
          the Pledge Agreement (as defined below);

     (b)  executed originals of that certain amendment to the partnership
          agreement of Merieux OraVax Co., a Delaware General Partnership
          ("Merieux"), relating to changes in the ownership of Merieux following
          the date thereof in form and substance acceptable to the Lender;

     (c)  certified copies of the Borrower's articles of incorporation, bylaws,
          partnership agreement or other organizational documents;

     (d)  a certified copy of resolutions of the Borrower's board of directors
          or other governing body authorizing the entering into of the Facility
          by the Borrower and the execution, delivery and performance by the
          Borrower of the Facility Documents;

     (e)  a certified copy of an incumbency certificate of the Borrower
          certifying that the officers or other representatives executing and
          delivering the Facility Documents on behalf of the Borrower are duly
          elected or appointed officers or representatives of the Borrower with
          authority to bind the Borrower with respect to such Facility Documents
          and the transactions contemplated thereby;

     (f)  all other resolutions, authorizations, approvals, powers, consents,
          licenses and documents as may be necessary or otherwise required by
          the Lender.

     (g)  at the time of making such Loan and after giving effect thereto, no
          Event of Default (as defined below) or any event or circumstance
          which, with the giving of notice or the lapse of time or both, would
          constitute an Event of Default (a "Default") has occurred or is
          continuing with respect to the Borrower under any of the Facility
          Documents.


                                       3

<PAGE>   8


     7. COLLATERAL DOCUMENTS. All of the Borrower's obligations from time to
time outstanding in respect of the Facility, this Agreement and the other
Facility Documents (collectively, the "Obligations") at all times shall be
secured by the collateral arrangements set forth in the Pledge Agreement between
the Lender and the Borrower in form and substance acceptable to the Lender
pledging the Borrower's interest in Merieux and Merieux OraVax S.N.C., a societe
en nom collectif organized under the laws of France ("Merieux France" and
together with Merieux, the "Partnerships") substantially in the form of Exhibit
B hereto (the "Pledge Agreement").

     8. REPRESENTATIONS AND WARRANTIES. The Borrower represents and warrants to
the Lender (which representations and warranties will be deemed to be repeated
by the Borrower on each day on which the Loan or other obligations of the
Borrower remain outstanding pursuant to this Agreement or any of the other
Facility Documents) that:

     (a)  It is a corporation duly organized, validly existing and in good
          standing under the laws of Delaware;

     (b)  It is duly qualified, in good standing and authorized to do business
          in each jurisdiction to the extent required by applicable law,
          regulation or rule, except where the failure to do so does not in the
          aggregate have a material adverse effect on the business or financial
          condition of the Borrower and its subsidiaries taken as a whole;

     (c)  It has the power to enter into each Facility and to execute each of
          the Facility Documents, to deliver each of the Facility Documents and
          to perform its obligations under each of the Facility Documents, and
          has taken all necessary action to authorize such execution, delivery
          and performance;

     (d)  Each of the Facility Documents has been duly executed and delivered on
          behalf of the Borrower;

     (e)  The execution, delivery and performance of each of the Facility
          Documents by the Borrower do not and will not violate or conflict with
          any law applicable to it, any provision of its organizational
          documents, any order or judgment of any court or other agency of
          government applicable to it or any of its assets or any contractual
          restriction binding on or affecting it or any of its assets;

     (f)  All governmental and other consents, authorizations, approvals,
          licenses and orders that are required to have been obtained by it with
          respect to the Facility Documents and the transactions contemplated
          thereby have been obtained and are in full force and effect and all
          conditions of any such consents, authorizations, approvals, licenses
          and orders have been complied with;


                                       4


<PAGE>   9


     (g)  Neither the making of the Loan, nor the application of the proceeds of
          the Loan will violate or be inconsistent with the provisions of
          Regulations T, U or X of the Board of Governors of the Federal Reserve
          System (the "Margin Regulations");

     (h)  Its obligations under each of the Facility Documents constitute its
          legal, valid and binding obligations, enforceable in accordance with
          their respective terms (subject to applicable bankruptcy,
          reorganization, insolvency, moratorium or similar laws affecting
          creditors' rights generally and subject, as to enforceability, to
          equitable principles of general application (regardless of whether
          enforcement is sought in a proceeding in equity or at law));

     (i)  No Event of Default or Default has occurred or is continuing, and no
          such Event of Default or Default would occur as a result of its
          entering into or performing its obligations under any of the Facility
          Documents;

     (j)  There is not pending or, to its knowledge, threatened against it,
          Parent or any of their respective subsidiaries any action, suit or
          proceeding at law or in equity or before any court, tribunal,
          governmental body, agency or official or any arbitrator that is likely
          to affect (1) the legality, validity or enforceability against the
          Borrower of any of the Facility Documents or its ability to perform
          its obligations under any of the Facility Documents or (2) in a
          materially adverse way, the operations, business, property or assets
          or financial or other condition of the Borrower, Parent and their
          respective subsidiaries, taken as a whole; and

     (k)  The Pledge Agreement constitutes a valid and binding agreement in
          accordance with its respective terms; the liens and security interests
          granted to the Lender pursuant to the Pledge Agreement to secure the
          Obligations constitute a first perfected priority lien and security
          interest on and in the Collateral subject thereto and all certificates
          evidencing the Collateral have been delivered to the Lender pursuant
          to the Pledge Agreement; all Collateral delivered or transferred to
          the Lender in respect of the Pledge Agreement is owned, legally and
          beneficially, solely by the Borrower, and such Collateral is not
          subject to any prior or existing mortgage, lien, charge, security
          interest, assignment or other encumbrance (other than in favor of the
          Lender pursuant to the Pledge Agreement).

     9. COVENANTS. The Borrower covenants to the Lender that, so long as the
Borrower has or may have any obligation under any of the Facility Documents:

     (a)  It will, and will cause each of its subsidiaries to, maintain in full
          force and effect and comply with all consents, authorizations,


                                       5


<PAGE>   10


          approvals, licenses and orders of any governmental or other authority
          that are required to be obtained by each of them with respect to any
          of the Facility Documents or the transactions contemplated thereby and
          will use all reasonable efforts to obtain any such consents,
          authorizations, approvals, licenses and orders that may become
          necessary in the future;

     (b)  It will, and will cause each of its subsidiaries to, comply in all
          material respects with all applicable laws and orders to which it may
          be subject if failure so to comply would materially adversely affect
          their respective business, operations or prospects or impair the
          Borrower's ability to perform its obligations under any of the
          Facility Documents;

     (c)  It will notify the Lender immediately upon the occurrence of a Default
          or an Event of Default;

     (d)  It will provide to the Lender its audited annual report and other
          financial reports as are regularly published an publicly available or
          filed with the Securities Exchange Commission and all quarterly
          financial reports, as soon as such reports are made publicly
          available; such reports shall be prepared in accordance with generally
          accepted accounting principles, consistently applied, in the United
          States of America;

     (e)  It will not use the proceeds of the Loan in any manner that would
          cause such borrowing or the application of such proceeds to violate
          the Margin Regulations or any other applicable law, rule or
          regulation;

     (f)  It will not create or permit to subsist any mortgage, lien, charge,
          security interest, assignment or other encumbrance whatsoever in or
          over any of the Collateral delivered or transferred to the Lender from
          time to time pursuant to this Agreement or the Pledge Agreement to
          secure the Obligations; and

     (g)  It will not sell, transfer or otherwise dispose of any of its right,
          title or interest in respect of any Collateral delivered or
          transferred to the Lender from time to time pursuant to this Agreement
          or the Pledge Agreement to secure the Obligations, except in
          accordance with this Agreement and the Pledge Agreement nor will it
          permit any of its subsidiaries to sell, transfer or otherwise dispose
          of any of its assets or properties, except in accordance with this
          Agreement and the Pledge Agreement.


                                       6


<PAGE>   11
     10. EVENTS OF DEFAULT AND REMEDIES. The occurrence of any of the following
events or conditions shall constitute an event of default (an "Event of
Default") with respect to the Borrower under this Agreement:

     (a)  Any amounts due under any of the Facility Documents are not paid when
          due;

     (b)  (i) Any event of default occurs and is continuing with respect to any
          of the Facility Documents other than this Agreement or (ii) the
          failure or refusal of the Borrower to properly perform, observe or
          comply with any condition, obligation, covenant or agreement (other
          than an obligation specified in clause (a) or (h)) to be performed,
          observed or complied with by the Borrower in any of the Facility
          Documents, and such failure or refusal continues for a period of
          thirty (30) days, or for such lesser period as stipulated in any of
          such Facility Documents, after written notice thereof from the Lender;

     (c)  A representation made or repeated or deemed to have been made or
          repeated by the Borrower in this Agreement or in any other Facility
          Document proves to have been incorrect or misleading in any material
          respect when made or repeated or deemed to have been made or repeated;

     (d)  The Borrower, Parent, either of the Partnerships or any of their
          respective subsidiaries (i) is dissolved (other than pursuant to a
          consolidation, amalgamation or merger); (ii) becomes insolvent or is
          unable to pay its debts or fails or admits in writing its inability
          generally to pay its debts as they become due; (iii) makes a general
          assignment, arrangement or composition with or for the benefit of its
          creditors; (iv) institutes or has instituted against it a proceeding
          seeking a judgment of insolvency or bankruptcy or any other relief
          under any bankruptcy or insolvency law or other similar law affecting
          creditors' rights, or a petition is presented for its winding-up or
          liquidation which is not dismissed, discharged, stayed or restrained
          within thirty (30) days of the institution or presentation thereof;
          (v) has a resolution passed for its winding-up, official management or
          liquidation (other than pursuant to a consolidation, amalgamation or
          merger); (vi) seeks or becomes subject to the appointment of an
          administrator, provisional liquidator, conservator, receiver, trustee,
          custodian or other similar official for it or for all or substantially
          all its assets; (vii) has a distress, execution, attachment,
          sequestration or other legal process levied, enforced or sued on
          against all or substantially all its assets and such process is not
          dismissed, discharged, stayed or restrained, in each case within
          thirty (30) days thereafter; (viii) causes or is subject to any event
          with respect to it which, under the applicable 


                                       7

<PAGE>   12

          laws of any jurisdiction, has an analogous effect to any of the events
          specified in clauses (i) to (vii) (inclusive); or (ix) takes any
          action in furtherance of, or indicating its consent to, approval of,
          or acquiescence in, any of the foregoing acts;

     (e)  Any person shall beneficially own, directly or indirectly, 25% or more
          of the common stock of the Borrower or Parent, or any Person shall
          have the power, direct or indirect, to vote securities having 25% or
          more of the ordinary voting power for the election of directors of the
          Borrower or the Parent, or shall beneficially own, directly or
          indirectly, securities having such power, or Borrower or Parent is a
          party to any merger, amalgamation or consolidation with any other
          entity which is consummated and following which the shareholders of
          Borrower or Parent (as applicable) immediately prior to such merger,
          amalgamation or consolidation cease to own beneficially, directly or
          indirectly, greater than 75% of the surviving company in such merger,
          amalgamation or consolidation following any such transaction;

     (f)  The Borrower or Parent defaults in the observance or performance of
          any condition, obligation, covenant or agreement relating to any of
          Borrower's or Parent's (which may, but not need be, owing to the
          Lender) (and such default continues for a period sufficient to permit
          the acceleration of the maturity thereof, whether or not such
          acceleration occurs);

     (g)  The Borrower, Parent or either of the Partnerships is a party to any
          merger, amalgamation or consolidation which is consummated or
          transfers all or substantially all its assets to another person or
          entity without the prior written consent of the Lender and, pursuant
          to such merger, amalgamation, consolidation or transfer, the
          creditworthiness of the resulting, surviving or transferee entity is
          materially weaker than that of the Borrower, Parent or such
          Partnership, respectively, immediately prior to such action;

     (h)  The failure or refusal of the Borrower to properly perform, observe or
          comply with (i) any of its obligations, covenants and agreement in
          connection with the amendment of the status of Merieux France
          including the making of any filings or other obligations required by
          the laws of any relevant jurisdictions to amend the status in a
          manner in form and substance satisfactory to the Lender and (ii) any
          of its obligations under the Pledge Agreement or otherwise to perfect
          the Lender's security interest created by the Pledge Agreement under
          the laws of France; and such failure or refusal continues for a period
          of fifteen (15) days after notice thereof from the Lender.



                                       8


<PAGE>   13


     (i)  (i) The failure or refusal of the Borrower to properly perform,
          observe or comply with any material condition, obligation, covenant or
          agreement (other than an obligation specified in clause (a)) to be
          complied with or performed or observed by it in accordance with the
          Pledge Agreement if such failure is continuing after any applicable
          grace period has elapsed; (ii) the expiration or termination of the
          Pledge Agreement or the failing or ceasing of the Pledge Agreement to
          be in full force and effect or for the liens created thereby to
          constitute first priority perfected liens for the purpose of this
          Agreement (in any case other than in accordance with its terms) prior
          to the payment of all Obligations; or (iii) the Borrower disaffirms,
          disclaims, repudiates or rejects, in whole or in part, or challenges
          the validity of, the Pledge Agreement.

     Upon the occurrence and during the continuance of an Event of Default, the
Lender will have the option, upon notice to the Borrower, of declaring the Loan,
together with unpaid accrued interest thereon, and any or all other amounts
payable to the Lender under the Facility Documents or otherwise to be
immediately due and payable and/or exercising its rights and remedies against
any Collateral or any other person or entity pursuant to the Pledge Agreement;
provided, however, that if an Event of Default specified in clause (d) shall
occur, no such notice need be given by the Lender to the Borrower.

     11. TAXES AND EXPENSES. (a) All payments made by the Borrower in respect of
principal of, and interest on, the Loan and all other amounts payable in respect
of other the Facility Documents or otherwise will be made without set-off,
counterclaim or other defense and will be made free and clear of, and without
deduction or withholding for, any present or future taxes, levies, imposts,
duties, fees, assessments or other charges of whatever nature now or hereafter
imposed by any jurisdiction or by any political subdivision or taxing authority
thereof or therein and all interest, penalties or similar liabilities with
respect thereto (collectively, the "Taxes"). The Borrower shall pay on demand
all stamp, documentary and other similar duties and taxes, if any, to which any
Facility Document from time to time may be subject or give rise. If the Borrower
is required by applicable law to make any deduction or withholding on any
payment as described above in respect of Taxes or otherwise, the Borrower shall:
(i) promptly notify the Lender of such occurrence; (ii) pay to the relevant
taxation or other authorities the full amount of the deduction or withholding
within the time allowed; (iii) furnish to the Lender within thirty (30) days of
such payment, an official receipt from such authorities for all amounts so
deducted or withheld; and (iv) pay to the Lender an additional amount so that
the Lender receives on the due date of such payment the full amount the Lender
would have received had no such deduction or withholding taken place.

     Subject to the Lender's compliance with its obligations to deliver certain
forms, certificates and documents as set forth in this paragraph, the Borrower
will indemnify and hold harmless the Lender, and reimburse the Lender upon its
written request, for the amount of any Taxes so levied or imposed and paid by
the Lender, other than Taxes imposed on or measured by the net income of the
Lender pursuant to the laws of the jurisdiction in which


                                       9


<PAGE>   14


the principal office of the Lender is located or under the laws of any political
subdivision or taxing authority of any such jurisdiction. Upon demand by the
Borrower, the Lender shall, as soon as practicable, deliver to the Borrower or
to such government or taxing authority as the Borrower reasonably directs, any
form, certificate or document which the Lender is entitled as a matter of law to
deliver that may be requested in order to allow the Borrower to make payments in
respect of the Loans and all other amounts payable in respect of the Facility
Documents without any deduction or withholding for or on account of any Taxes or
with such deduction or withholding at a reduced rate.

          (b) The Borrower agrees to pay on demand all of the Lender's
reasonable costs and expenses, including, without limitation, reasonable
attorneys' fees, in connection with the collection of any sums due to the Lender
and the enforcement, protection or perfection of its rights or interests
hereunder and under the Facility Documents.

     12. GOVERNING LAW. THIS AGREEMENT SHALL BE GOVERNED BY AND CONSTRUED IN
ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK WITHOUT REGARD TO ITS CONFLICT
OF LAW RULES.

     13. JURISDICTION. With respect to any suit, action or proceeding relating
to this Agreement or any of the other Facility Documents, the Borrower
irrevocably (a) submits to the non-exclusive jurisdiction of the courts in the
State of New York and the United States District Court located in the Borough of
Manhattan in New York City; and (b) waives any objection which it may have at
any time to the laying of venue of any such suit, action or proceeding brought
in any such court, waives any claim that any such suit, action or proceeding has
been brought in an inconvenient forum and further waives the right to object
with respect to any such suit, action or proceeding that such court does not
have any jurisdiction over it.

     Nothing contained in this Section 13 shall limit or impair the right of the
Lender to institute any suit, action, motion or proceeding in any other court of
competent jurisdiction, nor shall the taking of any suit, action or proceeding
in one or more jurisdictions preclude the taking of proceedings in any other
jurisdiction, whether concurrently or not.

     14. SERVICE OF PROCESS. The Borrower irrevocably appoints the following
process agent to receive, for it and on its behalf, service of process in any
suit, action or proceeding relating to this Agreement or any of the other
Facility Documents to which it is a party: CT Corporation System, 1633 Broadway,
New York, New York 10019. If for any reason the Borrower's process agent is
unable to act as such, the Borrower will promptly notify the Lender and within
thirty (30) days appoint a substitute process agent acceptable to the Lender.
Nothing in this Agreement will affect the right of the Lender to serve process
in any other manner permitted by law.

     15. WAIVER OF JURY TRIAL. THE BORROWER HEREBY IRREVOCABLY WAIVES ALL RIGHT
TO TRIAL BY JURY IN ANY SUIT, ACTION OR PROCEEDING ARISING OUT OF OR RELATING TO
THIS AGREEMENT OR ANY OF THE OTHER FACILITY DOCUMENTS.


                                       10


<PAGE>   15


     16. RIGHT OF SET-OFF. In addition to any rights or remedies now or
hereafter granted under applicable law or otherwise, the Lender, without any
notice whatsoever to the Borrower, may (but shall not be obliged to) set-off
against any obligation of the Borrower due and payable by the Borrower under any
of the Facility Documents any moneys held by the Lender for the account of the
Borrower and in any currency whether or not such monies are then due and
payable.

     17. AMENDMENTS, MODIFICATIONS, WAIVERS, ETC. No amendment, modification or
waiver of any provision of this Agreement or any of the other Facility Documents
and no consent by the Lender to any departure therefrom shall be effective
unless such amendment, modification or waiver shall be in writing and signed by
a duly authorized officer of the Lender, and the same shall then be effective
only for the period and on the conditions and for the specified instances
specified in writing. No failure or delay by the Lender in exercising any right,
power, remedy or privilege hereunder or under any of the Facility Documents
shall operate as a waiver thereof; nor shall any single or partial exercise
thereof preclude any subsequent or further exercises thereof or the exercise of
any other right, power, remedy or privilege. The rights, powers, remedies and
privileges provided in this Agreement and the other Facility Documents to the
Lender are cumulative and not exclusive of any rights, powers, remedies and
privileges provided by law or otherwise.

     18. NOTICES. All notifications, requests, demands and other communications
hereunder to either the Lender or the Borrower shall be in writing (unless
otherwise specified herein) and given to the address(es) or facsimile number(s)
set forth under the signatures of the parties hereto. Such notifications,
requests, demands and other communications shall be deemed effective (a) if sent
by mail five Business Days after having been deposited in the mails first class
postage prepaid (airmail if international) in an envelope addressed as
aforesaid, or (b) if sent to an officer of the recipient, at the time of
delivery to such officer, or (c) if sent by facsimile, when that transmission is
received by the recipient in legible form.

     19. ENTIRE AGREEMENT. This Agreement and the other Facility Documents
constitute the entire agreement and understanding of the parties with respect to
the subject matter hereof and thereof and supersedes all oral communication and
prior writings with respect thereto.

     20. COUNTERPARTS. This Agreement may be executed and delivered in
counterparts, each of which, when so executed and delivered, will be deemed an
original and all of which, taken together, shall constitute one instrument.

     21. SUCCESSORS AND ASSIGNS. The Borrower may not assign any of its rights
or delegate any of its obligations under this Agreement or any of the other
Facility Documents (or any part thereof) without the prior written consent of
the Lender. Other than an assignment to an affiliate of the Lender, the Lender
may not assign its rights and obligations hereunder without the consent of the
Borrower. The Lender shall, without the consent of the Borrower, have the right
at any time to sell, assign or transfer all of its rights and obligations
hereunder to any affiliate of the Lender. The Lender shall, upon 


                                       11


<PAGE>   16


the effectiveness of such assignment, surrender the Note to the Borrower for
cancellation and thereupon a new Note shall be issued and executed by the
Borrower to the assignee substantially in the form of the Note.

     22. EFFECTIVE DATE. This Agreement shall become effective as of November 2,
1998 (the "Effective Date"), if accepted by the Borrower as evidenced by its
signature below.








                                       12



<PAGE>   17


                               Respectfully,


                               CONNAUGHT LABORATORIES, INC.



                               By: /s/ Herve Tainturier  
                                  -----------------------------
                                  Print Name: Herve Tainturier
                                  Title:


                               Lender's Address: Route 611
                                                 Swiftwater, PA  18370
                               Telephone:        717-839-5587
                               Facsimile:        717-839-4096
                               Attention:        Vice President and General 
                                                 Counsel





AGREED AND ACCEPTED 
as of November 2, 1998:


ORAVAX JVM, INC.

By: /s/ Brigid A. Makes                                
   ----------------------------------------------
   Print Name: Brigid A. Makes
   Title: Treasurer

Borrower's Address:  38 Sidney Street, Cambridge, MA 02139
Telephone: 617-494-1339
Facsimile: 617-494-1741
Attention: Brigid A. Makes