Document:

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                                                                  EXHIBIT 10.34

                     EXECUTIVE SEVERANCE BENEFITS AGREEMENT

     THIS EXECUTIVE SEVERANCE BENEFITS AGREEMENT (the "Agreement") is entered
into effective as of the 23rd day of October 2000, between HARRY GREENBERG,
("Executive") and AVIRON, a Delaware corporation (the "Company"). This Agreement
is intended to provide Executive with the severance benefits described herein
upon the occurrence of specific events. Certain capitalized terms used in this
Agreement are defined in Article 6.

     The Company and Executive hereby agree as follows:

                                   ARTICLE 1

                            EMPLOYMENT BY THE COMPANY

     1.1 Upon execution of the offer letter of even date herewith (the "Offer
Letter"), Executive shall be employed as Senior Vice President and Chief
Scientific Officer.

     1.2 The Company and Executive wish to set forth the severance benefits
which Executive shall be entitled to receive in the event Executive's employment
with the Company terminates under the circumstances described herein.

     1.3 The duties and obligations of the Company to Executive under this
Agreement shall be in consideration for Executive's agreeing to the terms of the
Offer Letter with the Company, Executive's employment with the Company, and
Executive execution of the general waiver and release described in Section 4.2.

     1.4 This Agreement shall remain in full force and effect so long as
Executive is employed by the Company; provided, however, that Executive's rights
to payments and benefits under Article 2 or Article 3 shall continue until the
Company's obligation to provide such payments and benefits is satisfied.

                                   ARTICLE 2

                               SEVERANCE BENEFITS

     2.1 TERMINATION EVENTS. If Executive's employment involuntarily terminates
for any reason other than for Cause, Executive shall be entitled to receive the
following benefits set forth in Sections 2.2, 2.3 and 2.4.

     2.2 SALARY CONTINUATION. Executive shall receive Base Salary that has
accrued but is unpaid as of the date of a Covered Termination, and, within
thirty (30) days following such Covered Termination, Executive shall also
receive payments equal to six (6) months of Base Salary.

<PAGE>   2

     2.3 HEALTH INSURANCE COVERAGE.

          Provided that Executive makes a timely election to continue coverage
under the Company's group health plan pursuant to the Consolidated Omnibus
Budget Reconciliation Act of 1985 ("COBRA") in connection with Executive's
Covered Termination, the Company will pay Executive's COBRA premiums for a
maximum period of six (6) months following the date of such Covered Termination
(the "COBRA Continuation Period"). In addition, if Executive's spouse and/or
dependents were enrolled in the Company's group health plan on the date of the
Covered Termination, the Company will pay the COBRA premiums for Executive's
dependents during the COBRA Continuation Period, but only to the same extent
that such dependents' premiums under such plan were paid by the Company prior to
the date of such Covered Termination. No provision of this Agreement will affect
the continuation coverage rules under COBRA, except that the Company's payment
of any applicable premiums during the COBRA Continuation Period will be credited
as payment by Executive for purposes of the Executive's payment required under
COBRA. Therefore, the period during which Executive must elect to continue the
Company's group health coverage at his or her own expense under COBRA, the
length of time during which COBRA coverage will be made available to Executive,
and all other rights and obligations of the Executive under COBRA (except the
obligation to pay premiums that the Company pays during the COBRA Continuation
Period) will be applied in the same manner that such rules would apply in the
absence of this Agreement. At the conclusion of the COBRA Continuation Period,
Executive will be responsible for the entire payment of premiums required under
COBRA for the remaining duration of eligibility for COBRA, if any.

          Notwithstanding the foregoing, the Company's obligation to make COBRA
payments for Executive as described above shall cease immediately. if Executive
becomes eligible for other health insurance benefits at the expense of a new
employer. Executive agrees to notify a duly authorized officer of the Company,
in writing, Immediately upon acceptance of any employment following his
termination which provides Executive with eligibility for health insurance
benefits.

     2.4 VESTING OF OUTSTANDING OPTIONS. Outstanding, unvested stock options to
purchase common stock of the Company granted to Executive prior to the date of
the Covered Termination, either pursuant to the terms of the Offer Letter or
under the Company's discretionary stock compensation plans shall continue to
vest according the vesting schedule(s) in effect immediately prior to the date
of the Covered Termination for a period of up to six (6) months. Any stock
options that remain unvested six (6) months after the date of the Covered
Termination shall terminate. Options vesting through the "continuation" period
shall remain exercisable for up to 90 days after its conclusion.

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                                   ARTICLE 3

                                CHANGE OF CONTROL

     3.1 TERMINATION EVENTS. If Executive's employment terminates under
circumstances constituting a Covered Termination upon or within eighteen (18)
months following a Change of Control of the ownership of the Company, Executive
shall be entitled to receive the following benefits set forth in Sections 3.2,
3.3 and 3.4 and shall not receive any benefits under Article 2.

     3.2 SALARY CONTINUATION. Executive shall receive Base Salary that has
accrued but is unpaid as of the date of such Covered Termination, and, within
thirty (30) days following such Covered Termination, Executive also shall
receive a lump sum payment equal to one year of the base salary which Executive
was receiving immediately prior to the Change of Control Executive's targeted
bonus for the fiscal year in which the Change of Control occurs.

     3.3 HEALTH INSURANCE COVERAGE IN THE EVENT OF CHANGE OF CONTROL:

          Provided that Executive makes a timely election to continue coverage
under the Company's group health plan pursuant to the Consolidated Omnibus
Budget Reconciliation Act of 1985 ("COBRA") in connection with Executive's
Covered Termination, the Company will pay Executive's COBRA premiums for a
maximum period of one (1) year following the date of such Covered Termination
(the "COBRA Continuation Period"). In addition, if Executive's spouse and/or
dependents were enrolled in the Company's group health plan on the date of the
Covered Termination, the Company will pay the COBRA premiums for Executive's
dependents during the COBRA Continuation Period, but only to the same extent
that such dependents' premiums under such plan were paid by the Company prior to
the date of such Covered Termination. No provision of this Agreement will affect
the continuation coverage rules under COBRA, except that the Company's payment
of any applicable premiums during the COBRA Continuation Period will be credited
as payment by Executive for purposes of the Executive's payment required under
COBRA. Therefore, the period during which Executive must elect to continue the
Company's group health coverage at his or her own expense under COBRA, the
length of time during which COBRA coverage will be made available to Executive,
and all other rights and obligations of the Executive under COBRA (except the
obligation to pay premiums that the Company pays during the COBRA Continuation
Period) will be applied in the same manner that such rules would apply in the
absence of this Agreement. At the conclusion of the COBRA Continuation Period,
Executive will be responsible for the entire payment of premiums required under
COBRA for the remaining duration of eligibility for COBRA, if any.

          Notwithstanding the foregoing, the Company's obligation to make COBRA
payments for Executive shall cease immediately if Executive becomes eligible for
other health insurance benefits at the expense of a new employer. Executive
agrees to notify a duly authorized officer of the Company, in writing,
immediately upon acceptance of any employment following the Covered Termination
which provides Executive with eligibility for health insurance benefits.

<PAGE>   4

     3.4 ACCELERATION OF VESTING OF OUTSTANDING OPTIONS. In the event of a
Covered Termination where the Company has assumed or substituted the Employee's
options in connection with the Change of Control, the vesting of outstanding
stock options to purchase common stock of the Company granted to Employee prior
to the date of termination of employment shall accelerate as of the date of such
Covered Termination so that all outstanding options are one hundred percent
(100%) vested and immediately exercisable. Such acceleration of vesting of
outstanding options also shall apply to any unvested option shares that were
acquired by Employee on or before the date of the Covered Termination and that
were subject to a repurchase option by the Company as of such date. Where the
Company does not assume or substitute the Employee's options in connection with
a Change of Control, one hundred percent (100%) of options will vest immediately
prior to a Change of Control.

     3.5 PARACHUTE PAYMENTS. In the event that the acceleration of the vesting
provided for in Section 3.4 and benefits otherwise payable to Executive (i)
constitute "parachute payments" within the meaning of Section 280G of the
Internal Revenue Code of 1986, as amended, (the "Code"), or any comparable
successor provision, and (ii) but for this Section would be subject to the
excise tax imposed by Section 4999 of the Code, or any comparable successor
provision (the "Excise Tax"), then Executive's benefits hereunder shall be
either

          (i)  provided to Executive in full, or

          (ii) provided to Executive as to such lesser extent which would result
               in no portion of such benefits being subject to the Excise Tax,

whichever of the foregoing amounts, when taking into account applicable federal,
state, local and foreign income and employment taxes, the Excise Tax, and any
other applicable taxes, results in the receipt by Executive, on an after-tax
basis, of the greatest amount of benefits, notwithstanding that all or some
portion of such benefits may be taxable under the Excise Tax. Unless the Company
and Executive otherwise agree in writing, any determination required under this
Section shall be made in writing in good faith by the Accountants. In the event
of a reduction of benefits hereunder, benefits payable in cash shall be reduced
first. For purposes of making the calculations required by this section, the
Accountants may make reasonable assumptions and approximations concerning
applicable taxes and may rely on reasonable, good faith interpretations
concerning the application of the Code, and other applicable legal authority.
The Company and Executive shall furnish to the Accountants such information and
documents as the Accountants may reasonably request in order to make a
determination under this section. The Company shall bear all costs the
Accountants may reasonably incur in connection with any calculations
contemplated by this section.

          If, notwithstanding any reduction described in this section, the IRS
determines that Executive is liable for the Excise Tax as a result of the
receipt of the payment of benefits as described above, then Executive shall be
obligated to pay back to the Company, within thirty (30) days after a final IRS
determination or in the event that Executive challenges the final IRS
determination, a final judicial determination, a portion of the payment equal to
the "Repayment Amount." The Repayment Amount with respect to the payment of
benefits shall be the smallest such amount, if any, as shall be required to be
paid to the Company so that Executive's net after tax proceeds with respect to
any payment of benefits (after taking into account the payment of

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the Excise Tax and all other applicable taxes imposed on such payment) shall be
maximized. The Repayment Amount with respect to the payment of benefits shall be
zero if a Repayment Amount of more than zero would not result in Executive's net
after-tax proceeds with respect to the payment of such benefits being maximized.
If the Excise Tax is not eliminated pursuant to this paragraph, Executive shall
pay the Excise Tax.

          Notwithstanding any other provision of this Section 3.5, if (i) there
is a reduction in the payment of benefits as described in this section, (ii) the
IRS later determines that Executive is liable for the Excise Tax, the payment of
which would result in the maximization of Executive's net after-tax proceeds
(calculated as if Executive's benefits had not previously been reduced), and
(iii) Executive pays the Excise Tax, then the Company shall pay to Executive
those benefits which were reduced pursuant to this Section contemporaneously or
as soon as administratively possible after Executive pays the Excise Tax so that
Executive's net after-tax proceeds with respect to the payment of benefits is
maximized.

                                   ARTICLE 4

                     LIMITATIONS AND CONDITIONS ON BENEFITS

     4.1 WITHHOLDING OF TAXES. The Company shall withhold appropriate federal,
state, local (and foreign, if applicable) income and employment taxes from any
payments hereunder.

     4.2 RELEASE PRIOR TO RECEIPT OF BENEFITS. Upon the occurrence of a Covered
Termination, and prior to the receipt of any benefits under this Agreement on
account of the occurrence of such Covered Termination, Executive shall execute a
release (the "Release") in the form incorporated herein and attached hereto as
Attachment I. Such Release shall specifically relate to all of Executive's
rights and claims in existence at the time of such execution and shall confirm
Executive's obligations under the Company's standard form of proprietary
information agreement. It is understood that Executive has twenty-one (21) days
to consider whether to execute such Release, and Executive may revoke such
Release within seven (7) business days after execution. In the event Executive
does not execute such Release within the twenty-one (2l)-day period, or if
Executive revokes such Release within the subsequent seven (7) business day
period, no benefits shall be payable under this Agreement and this Agreement
shall be null and void. Notwithstanding the foregoing, in addition to or in lieu
of the release contained in Attachment I, Executive may be required to execute
and deliver an effective release in such other form as the Company may, in its
sole discretion, determine to be necessary or appropriate in order to comply
with the requirements of the laws of any jurisdiction applicable to Executive in
order to make a general release of claims effective and enforceable.

                                   ARTICLE 5

                            OTHER RIGHTS AND BENEFITS

     5.1 NONEXCLUSIVITY. Except as otherwise expressly provided herein, nothing
in the Agreement shall prevent or limit Executive's continuing or future
participation in any benefit, bonus, incentive or other plans, programs,
policies or practices provided by the Company and for which Executive may
otherwise qualify, nor shall anything herein limit or otherwise affect such

<PAGE>   6

rights as Executive may have under other agreements with the Company. Except as
otherwise expressly provided herein, amounts which are vested benefits or which
Executive is otherwise entitled to receive under any plan, policy, practice or
program of the Company at or subsequent to the date of a Covered Termination
shall be payable in accordance with such plan, policy, practice or program.

     5.2 NON-DUPLICATION OF BENEFITS. Notwithstanding any other provision of the
Agreement to the contrary, any benefits payable to Executive under this
Agreement shall be in lieu of any severance benefits payable by the Company to
such individual under any other arrangement covering the individual, unless
expressly otherwise agreed to by the Company in writing.

                                    ARTICLE 6

                                   DEFINITIONS

     For purposes of the Agreement, the following terms are defined as follows:

     6.1 "ACCOUNTANTS" means the independent public accountants of the Company.

     6.2 DEFINITION OF BASE SALARY: Base Salary means the Executive's base
salary (exclusive of bonuses and other forms of supplemental compensation) at
the rate in effect during the last regularly scheduled payroll period
immediately preceding the date of Executive's Covered Termination or prior to
the Change of Control, unless a different time period for establishing Base
Salary is expressly set forth in this Agreement.

     6.3 "CAUSE" Executive's dismissal or discharge for fraud, misappropriation,
embezzlement or intentional misconduct on the part of Executive which resulted
in material loss, damage or injury to the Company,

     6.4 "CHANGE OF CONTROL" means a (i) dissolution or liquidation of the
Company; (ii) a sale, lease or other disposition of all or substantially all of
the assets of the Company; (iii) a merger or consolidation in which the Company
is not the surviving corporation and in which beneficial ownership of securities
of the Company representing at least forty percent (40%) of the combined voting
power entitled to vote in the election of the members of the Board of Directors
has changed; (iv) a reverse merger in which the Company is the surviving
corporation but the shares of the Company's Common Stock outstanding immediately
preceding the merger are converted by virtue of the merger into other property,
whether in the form of securities, cash or otherwise, and in which beneficial
ownership of securities of the Company representing at least forty percent (40%)
of the combined voting power entitled to vote in the election of the member of
the Board of Directors has changed, (v) an acquisition by any entity (other than
(A) a controlled affiliate of the Company, (B) any employee benefit plan, or
related trust, sponsored or maintained by the Company or subsidiary of the
Company or other entity controlled by the Company, or (C) any company owned
directly or indirectly by stockholders of the Company in substantially the same
proportions as their ownership of Common Stock interest of the Company,
immediately prior to the occurrence with respect to which the evaluation of the
Change in Control is being made) of the beneficial ownership, directly or
indirectly, of securities of the

<PAGE>   7

Company representing at least forty percent (40%) of the combined voting power
of the Company's then outstanding securities; or (vi) in the event that the
individuals who, as of the date of adoption of the Plan, are members of the
Company's Board of Directors (the "Incumbent Board"), cease for any reason to
constitute at least forty percent (40%) of the Board of Directors. (If the
election, or nomination for election by the Company's stockholders, of any new
Director is approved by a vote of at least forty percent (40%) of the Incumbent
Board, such new Director shall be considered to be a member of the Incumbent
Board in the future.)

     6.5  "CODE" means the Internal Revenue Code of 1986, as amended.

     6.6 "COVERED TERMINATION" means involuntary termination by the Company of
Executive's employment with the Company for any reason other than death,
disability or for Cause or upon or within eighteen (18) months following a
Change of Control of the ownership of the Company, Executive voluntarily
terminates employment after any of the following are, undertaken without
Executive's express written consent:

          (a)  the assignment to Executive of any duties or responsibilities
which result in a material diminution or adverse change of Executive's position,
status or circumstances of employment;

          (b)  a reduction by the Company in Executive's Base Salary;

          (c)  any failure by the Company to continue in effect any benefit plan
or arrangement, including incentive plans or plans to receive securities of the
Company, in which Executive is participating (hereinafter referred to as
"Benefit Plans"), or the taking of any action by the Company which would
adversely affect Executive's participation in or reduce Executive's benefits
under any Benefit Plans or deprive Executive of any fringe benefit then enjoyed
by Executive; provided, however, a Covered Termination shall not exist under
this subSection 6.6(c) if the Company offers a range of benefit plans and
programs which, taken as a whole, are comparable to the Benefit Plans provided
to Executive as of the date of this Agreement, as determined in good faith by
the Company;

          (d)  a relocation of Executive or the Company's principal business
offices to a location more than twenty-five (25) miles from Mountain View,
California, at which Executive has performed duties, except for required travel
by Executive on the Company's business to an extent substantially consistent
with Executive's business travel obligations as of the date of this Agreement;

          (e)  any material breach by the Company of any provision of this
Agreement which is not cured by the Company within twenty (20) days of delivery
of written notice from Executive of such breach; or

          (f)  any failure by the Company to obtain the assumption of this
Agreement by any successor or assign of the Company.

<PAGE>   8

                                   ARTICLE 7

                               GENERAL PROVISIONS

     7.1  EMPLOYMENT STATUS. This Agreement, the Offer Letter, nor any
Attachment or exhibit to the Offer Letter do not constitute a contract of
employment or impose on Executive any obligation to remain as an employee, or
impose on the Company any obligation (i) to retain Executive as an employee,
(ii) to change the status of Executive as an at-will employee, or (iii) to
change the Company's policies regarding termination of employment; or (iv) to be
unable to terminate Executive's employment with the Company at any time, with or
without notice, for any reason or no reason.

     7.2  NOTICES. Any notices provided hereunder must be in writing and such
notices or any other written communication shall be deemed effective upon the
earlier of personal delivery (including delivery by facsimile) or the third day
after mailing by first class mail, to the Company at its primary office location
and to Executive at Executive's address as listed in the Company's payroll
records. Any payments made by the Company to Executive under the terms of this
Agreement shall be delivered to Executive either in person or at the address as
listed in the Company's payroll records.

     7.3  SEVERABILITY. If a legal authority of competent jurisdiction
determines that any term or provision of this Agreement is invalid or
unenforceable, in whole or in part, then the remaining terms and provisions
hereof shall be unimpaired. Such legal authority will have the authority to
modify or replace the invalid or unenforceable term or provision with a valid
and enforceable term or provision that most accurately embodies the parties'
intention with respect to the invalid or unenforceable term or provision.

     7.4  WAIVER. If either party should waive any breach of any provisions of
this Agreement, he or it shall not thereby be deemed to have waived any
preceding or succeeding breach of the same or any other provision of this
Agreement.

     7.5  COMPLETE AGREEMENT. This Agreement, including Attachment I, and any
other written agreements referred to in this Agreement, constitutes the entire
agreement between Executive and the Company and it is the complete, final, and
exclusive embodiment of their agreement with regard to this subject matter. It
is entered into without reliance on any promise or representation other than
those expressly contained herein.

     7.6  AMENDMENT OR TERMINATION OF AGREEMENT. This Agreement may be changed
or terminated only upon the mutual written consent of the Company and Executive.
The written consent of the Company to a change or termination of this Agreement
must be signed by an executive officer of the Company after such change or
termination has been approved by the Company's Board of Directors.

     7.7  COUNTERPARTS. This Agreement may be executed in separate counterparts,
any one of which need not contain signatures of more than one party, but all of
which taken together will constitute one and the same Agreement.

<PAGE>   9

     7.8  HEADINGS. The headings of the Articles and Sections hereof are
inserted for convenience only and shall not be deemed to constitute a part
hereof nor to affect the meaning hereof.

     7.9  SUCCESSORS AND ASSIGNS. This Agreement is intended to bind and inure
to the benefit of and be enforceable by Executive and the Company, and their
respective successors, assigns, heirs, executors and administrators, except that
Executive may not assign any duties hereunder and may not assign any rights
hereunder without the written consent of the Company, which consent shall not be
withheld unreasonably.

     7.10 ATTORNEYS' FEES. If either party hereto brings any action to enforce
his or its rights hereunder, the prevailing party in any such action shall be
entitled to recover his or its reasonable attorneys' fees and costs incurred in
connection with such action.

     7.11 CHOICE OF LAW. All questions concerning the construction, validity and
interpretation of this Agreement will be governed by the law of the State of
California, without regard to such state's conflict of laws rules.

     7.12 NON-PUBLICATION. The parties mutually agree not to disclose publicly
the terms of this Agreement except to the extent that disclosure is mandated by
applicable law or to respective personal advisors.

     7.13 CONSTRUCTION OF AGREEMENT. In the event of a conflict between the text
of this Agreement and any summary, description or other information regarding
this Agreement, the text of this Agreement shall control.

     IN   WITNESS WHEREOF, the parties have executed this Agreement on the day
and year written above.

AVIRON                                        HARRY GREENBERG

By: /s/ C. Boyd Clarke                        /s/ Harry Greenberg
    -----------------------------             -----------------------------

Name:    C.  Boyd Clarke
Title:   CEO and President<PAGE>   1

                                                                   EXHIBIT 10.38

[***] - CERTAIN CONFIDENTIAL INFORMATION CONTAINED IN THIS DOCUMENT, MARKED BY
[***] HAS BEEN OMITTED AND FILED SEPARATELY WITH THE SECURITIES AND EXCHANGE
COMMISSION PURSUANT TO RULE 24B-2 OF THE SECURITIES EXCHANGE ACT OF 1934, AS
AMENDED.

Dated                                                           October 11, 2000
--------------------------------------------------------------------------------

                           (1) EVANS VACCINES LIMITED

                              (2) AVIRON UK LIMITED

                                   (3) AVIRON

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

                               AGREEMENT FOR LEASE

                                       OF

                       AVU PREMISES AT GASKILL ROAD, SPEKE

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

                               CMS Cameron McKenna
                                   Mitre House
                              160 Aldersgate Street
                                 London EClA 4DD

                              T +44(0)20 7367 3000
                              F +44(0)20 7367 2000

<PAGE>   2

[***] - CERTAIN CONFIDENTIAL INFORMATION CONTAINED IN THIS DOCUMENT, MARKED BY
[***] HAS BEEN OMITTED AND FILED SEPARATELY WITH THE SECURITIES AND EXCHANGE
COMMISSION PURSUANT TO RULE 24B-2 OF THE SECURITIES EXCHANGE ACT OF 1934, AS
AMENDED.

                                TABLE OF CONTENTS

<TABLE>
<CAPTION>
                                                                                           PAGE
<S>                                                                                        <C>
1.   DEFINITIONS.............................................................................1

2.   GENERAL PROVISIONS......................................................................2

3.   STANDARD CONDITIONS.....................................................................2

4.   CONDITION PRECEDENT.....................................................................3

5.   TITLE...................................................................................3

6.   MATTERS SUBJECT TO WHICH THE PREMISES WE LET............................................3

7.   THE LEASE...............................................................................3

8.   POSSESSION..............................................................................4

9.   ALIENATION..............................................................................4

10.  ACKNOWLEDGMENT AND INTEREST.............................................................4

11.  TERMINATION.............................................................................4

12.  INDEMNITY...............................................................................6

13.  [***]...................................................................................6

14.  SURETY..................................................................................6

15.  DISPUTES................................................................................7

16.  JURISDICTION............................................................................7

17.  THIRD PARTY RIGHTS......................................................................7
</TABLE>

                                       i

<PAGE>   3

THIS AGREEMENT is made                                                      2000
BETWEEN:

(1)     EVANS VACCINES LIMITED (registered number 3970089) having its registered
        office at 216 Bath Road, Slough, Berkshire SL1 4EN (the "LANDLORD") and

(2)     AVIRON UK LIMITED (registered number 3854275) having its registered
        office at Carmelite, 50 Victoria Embankment, London EC4Y 0DX (the
        "TENANT") and

(3)     AVIRON (registered in Delaware) having its registered office at 297
        North Bernardo Avenue, Mountain View, California 94043, United States of
        America (the "SURETY")

IT IS AGREED as follows:

1.      DEFINITIONS

        1.1    In this agreement unless the context otherwise requires the
               following expressions have the following meanings:

               "COMPETENT AUTHORITY": any local authority or any other body
               exercising powers under statute or by Royal Charter or any
               utility service or supply company

               "COMPLIANCE DATE": the date on which the Condition Precedent are
               wholly fulfilled

               "CONDITION PRECEDENT":

                      (a)    the grant of the Exclusion Order

               "CUT-OFF DATE": 30 April 2001 ([***])

               "EXCLUSION ORDER": an order of a competent court under the
               provisions of section 38(4) of the Landlord and Tenant Act 1954
               (as amended by section 5 of the Law of Property Act 1969)
               authorizing the Landlord and the Tenant to agree that the
               provisions of sections 24-28 of that Act win be excluded in
               relation to the tenancy to be created by the Lease

               "LANDLORD'S SOLICITORS": [***]

               "LEASE": an underlease in the form of the draft annexed hereto
               subject to such amendments as the Landlord may require and the
               Tenant may approve (such approval not to be unreasonably withheld
               or delayed)

               "PREMISES": that part of the building known as AVU Unit, Gaskill
               Road and more particularly described in the Lease

[***] - CERTAIN CONFIDENTIAL INFORMATION CONTAINED IN THIS DOCUMENT, MARKED BY
[***] HAS BEEN OMITTED AND FILED SEPARATELY WITH THE SECURITIES AND EXCHANGE
COMMISSION PURSUANT TO RULE 24B-2 OF THE SECURITIES EXCHANGE ACT OF 1934, AS
AMENDED.

                                       1
<PAGE>   4

               "REGISTERED TITLE": the tides numbered MS134921, MS253780 and
               MS5387854 at HM Land Registry

               "RENT COMMENCEMENT DATE": the date of completion of the Lease

               "STANDARD CONDITIONS": the Standard Conditions of Sale (Third
               Edition)

               "TENANT'S SOLICITORS": [***]

               "VAT": Value Added Tax and any tax or duty of a similar nature
               substituted for or in addition to it

        1.2    The definitions in the Standard Conditions also apply in this
               agreement

2.      GENERAL PROVISIONS

        2.1    In this agreement unless the context otherwise requires
               references to clauses and schedules are to clauses of and
               schedules to this agreement

        2.2    The headings to clauses and other parts of this agreement do not
               affect its construction

        2.3    This agreement contains the whole agreement between the parties
               relating to the matters herein mentioned and supersedes previous
               agreements between them (if any) relating thereto

        2.4    This agreement may only be varied in writing signed by or on
               behalf of the parties

        2.5    The Tenant acknowledges that it has not entered into this
               agreement in reliance upon representations made by or on behalf
               of the Landlord other than in respect of such reliance as may be
               placed upon the Landlord's Solicitors' written replies to the
               Tenant's Solicitors' preliminary enquiries

        2.6    Nothing in this agreement is to be read or construed as excluding
               any liability or remedy resulting from fraudulent
               misrepresentation

        2.7    All money payable by the Tenant under this agreement will be paid
               by direct credit transfer for the credit of the Landlord's
               Solicitors' clients' account at [***] or for the credit of any
               other bank account specified in writing by the Landlord's
               Solicitors

3.      STANDARD CONDITIONS

        This agreement incorporates the Standard Conditions as varied by the
        schedule and so far as they apply to a letting and are not varied by or
        inconsistent with the other provisions of this agreement (which will
        prevail in case of conflict)

[***] - CERTAIN CONFIDENTIAL INFORMATION CONTAINED IN THIS DOCUMENT, MARKED BY
[***] HAS BEEN OMITTED AND FILED SEPARATELY WITH THE SECURITIES AND EXCHANGE
COMMISSION PURSUANT TO RULE 24B-2 OF THE SECURITIES EXCHANGE ACT OF 1934, AS
AMENDED.

                                       2
<PAGE>   5

4.      CONDITION PRECEDENT

        4.1    The grant of the Lease is conditional on the Condition Precedent
               being wholly fulfilled

        4.2    The parties will apply for and use all reasonable endeavours to
               procure that the Condition Precedent is wholly fulfilled

5.      TITLE

        5.1    Title to the Premises will not be deduced but the Tenant will
               nevertheless be deemed to take the Lease with full knowledge of
               the terms and contents of and of any matter referred to in or
               deriving from the Registered Title and will raise no requisition
               on them

6.      MATTERS SUBJECT TO WHICH THE PREMISES WE LET

        6.1    The Premises are let subject to and as the case may be with the
               benefit of the matters contained or referred to in the Lease

        6.2    The Premises are also let subject to:

               6.2.1  all matters registrable by any Competent Authority
                      pursuant to statute

               6.2.2  all requirements notices orders or proposals (whether or
                      not subject to confirmation) of any Competent Authority

               6.2.3  all matters disclosed or reasonably to be expected to be
                      disclosed by [***] or as the result of [***] and whether
                      made in person by writing or orally by or for the Tenant
                      or [***]

               6.2.4  all notices served by [***]

7.      THE LEASE

        7.1    The Landlord will grant or procure the grant of and the Tenant
               will accept the Lease within [***] from and including the
               Compliance Date

        7.2    The Lease will be for a term of approximately 5 years from and
               including the date of actual completion of the Lease and expiring
               on 30th June 2006

        7.3    The initial annual rent first reserved by the Lease will from and
               including the Rent Commencement Date be [***]

        7.4    The Tenant will on the date for completion of the Lease in
               accordance with clause 7.1 pay to the Landlord:

[***] - CERTAIN CONFIDENTIAL INFORMATION CONTAINED IN THIS DOCUMENT, MARKED BY
[***] HAS BEEN OMITTED AND FILED SEPARATELY WITH THE SECURITIES AND EXCHANGE
COMMISSION PURSUANT TO RULE 24B-2 OF THE SECURITIES EXCHANGE ACT OF 1934, AS
AMENDED.

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               7.4.1  any proportion of the rent first reserved by and then
                      payable under the Lease for the period from and including
                      the Rent Commencement Date

               7.4.2  any other rents reserved by or money payable and then due
                      under the Lease calculated from and including the Rent
                      Commencement Date

8.      POSSESSION

        8.1    Until the date for completion of the Lease the Tenant may remain
               upon the Premises subject to the Tenant

               8.1.1  paying to the Landlord from and including the Rent
                      Commencement Date rent at the rate first reserved by the
                      Lease

               8.1.2  observing and performing the obligations on its part to be
                      contained in the Lease

        8.2    To the extent that the Tenant his exclusive possession of the
               Premises at any time prior to actual completion of the Lease the
               Tenant will hold the Premises as [***] of the Landlord

        8.3    If this agreement is determined then upon such determination the
               Tenant will [***] vacate the Premises (first making good all
               damage occasioned by its occupation and if and to the extent
               required by the Landlord reinstating the Premises to the
               reasonable satisfaction of the Landlord)

9.      ALIENATION

        The benefit of this agreement is [***] and the [***] will not [***] its
        interest under this agreement or any part thereof or otherwise [***]
        such interest or any part thereof and the Tenant named herein will [***]
        the Lease

10.     ACKNOWLEDGMENT AND INTEREST

        The Tenant acknowledges and agrees that without prejudice to any other
        right remedy or power of the Landlord if any sums have become due from
        the Tenant to the Landlord under this agreement but remain unpaid for a
        period exceeding [***] the Tenant will pay [***] to the Landlord [***]
        at [***] rate ([***] any judgment) from the date when they become due
        until payment thereof calculated on a daily basis and [***]

11.     TERMINATION

        11.1   If:

               11.1.1 there is any breach of the obligations of the Tenant
                      and/or the Surety under this agreement which (if capable
                      of remedy) is not remedied by the

[***] - CERTAIN CONFIDENTIAL INFORMATION CONTAINED IN THIS DOCUMENT, MARKED BY
[***] HAS BEEN OMITTED AND FILED SEPARATELY WITH THE SECURITIES AND EXCHANGE
COMMISSION PURSUANT TO RULE 24B-2 OF THE SECURITIES EXCHANGE ACT OF 1934, AS
AMENDED.

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                      Tenant and/or the Surety within such reasonable period as
                      the Landlord stipulates or

               11.1.2 the Tenant and/or the Surety (being a body corporate) is
                      unable to pay its debts (as defined in section 123 of the
                      Insolvency Act 1986) or has a winding-up petition or
                      petition for an administration order presented against it
                      or passes a winding up resolution (other than in
                      connection with a members' voluntary winding up for the
                      purposes of an amalgamation or reconstruction which has
                      the prior written approval of the Landlord) or calls a
                      meeting of its creditors to consider a resolution that it
                      be wound up voluntarily or resolves to present its own
                      winding-up petition or is wound up (whether in England or
                      elsewhere) or the directors or shareholders of the Tenant
                      or the Surety resolve to present a petition for an
                      administration order in respect of the Tenant or the
                      Surety (as the case may be) or an administrative receiver
                      or a receiver or a receiver and manager is appointed in
                      respect of the property or any part thereof of the Tenant
                      or the Surety or

               11.1.3 the Tenant and/or the Surety (being a body corporate)
                      calls or a nominee calls on its behalf a meeting of its
                      creditors or any of them or makes an application to the
                      court under section 425 of the Companies Act 1985 or
                      submits to its creditors or any of them a proposal
                      pursuant to Part I of the Insolvency Act 1986 or enters
                      into any arrangement scheme compromise moratorium or
                      composition with its creditors or any of them (whether
                      pursuant to Part I of the Insolvency Act 1986 or
                      otherwise) or

               11.1.4 the Tenant and/or the Surety (being an individual) makes
                      an application to the court for an interim order under
                      Part VIII of the Insolvency Act 1986 or convenes a meeting
                      of his creditors or any of them or enters into any
                      arrangement scheme compromise moratorium or composition
                      with his creditors or any of them (whether pursuant to
                      Part VIII of the Insolvency Act 1986 or otherwise) or has
                      a bankruptcy petition presented against him or is adjudged
                      bankrupt (whether in England or elsewhere)

        THEN and in any such case the Landlord may by notice in writing to the
        Tenant at any time thereafter terminate this agreement (without
        prejudice to any right or remedy of any party in respect of any
        antecedent breach of this agreement and without prejudice to any
        continuing obligations of the Surety under this agreement)

        11.2   If the Condition Precedent is not fulfilled prior to the Cut-Off
               Date the Landlord may determine this agreement by giving to the
               Tenant notice to that effect whereupon the Tenant will forthwith
               return all title and other documents furnished to it and remove
               any notice caution or land charge entry registered in respect of
               this agreement but such determination will be without prejudice
               to any

[***] - CERTAIN CONFIDENTIAL INFORMATION CONTAINED IN THIS DOCUMENT, MARKED BY
[***] HAS BEEN OMITTED AND FILED SEPARATELY WITH THE SECURITIES AND EXCHANGE
COMMISSION PURSUANT TO RULE 24B-2 OF THE SECURITIES EXCHANGE ACT OF 1934, AS
AMENDED.

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               tight or remedy of either party in respect of any antecedent
               breach of this agreement

12.     INDEMNITY

        The Tenant will indemnify the Landlord and any superior lessor against
        all actions proceedings claims demands losses costs expenses damages and
        liability (including any liability for any injury to any person or
        damage to any land or other property) arising directly or indirectly
        from any breach of any obligation of the Tenant under this agreement or
        any act or omission of the Tenant or [***]

13.     [***]

        13.1   All sums payable under the terms of this agreement are [***] in
               respect thereof howsoever arising and the Tenant will pay to the
               Landlord all [***] for which the Landlord or the Superior Lessor
               is liable to [***] in relation to any supply made or deemed to be
               made for [***] purposes pursuant to this agreement

        13.2   The Tenant does not intend or expect the Premises to be occupied
               by it or a person that is connected with the Tenant as determined
               in accordance with section [***] other than wholly or mainly for
               eligible purposes (within the meaning of paragraph [***])

        13.3   The Tenant represents warrants and undertakes to and with the
               Landlord that the statement in clause 13.2 is at the date of this
               agreement and will be at the date of completion of the Lease true
               and correct in all respects

14.     SURETY

        14.1   In consideration of the Landlord entering into this agreement at
               the request of the Surety the Surety will procure the observance
               and performance of all the obligations of the Tenant under this
               agreement and in the case of any default the Surety will observe
               and perform such obligations as if the Surety instead of the
               Tenant were liable therefor as a principal obligor and not merely
               as a surety and the Surety agrees with the Landlord as a primary
               obligation to keep the Landlord indemnified on demand against all
               losses damages costs and expenses incurred by the Landlord as a
               result of any failure by the Tenant to observe and perform such
               obligations or as a result of any obligation of the Tenant under
               this agreement being or becoming unenforceable

        14.2   If this agreement is disclaimed by or on behalf of the Tenant or
               is terminated in relation to the Tenant pursuant to clause 11.1
               the Surety will (if so required by the Landlord by written notice
               within three months after such disclaimer or after the date of
               the Landlord's notice of termination under clause 11.1 (as the
               case may be)) enter into a new agreement with the Landlord
               containing the same conditions and provisions as this agreement
               (except this clause 14) and the new agreement

[***] - CERTAIN CONFIDENTIAL INFORMATION CONTAINED IN THIS DOCUMENT, MARKED BY
[***] HAS BEEN OMITTED AND FILED SEPARATELY WITH THE SECURITIES AND EXCHANGE
COMMISSION PURSUANT TO RULE 24B-2 OF THE SECURITIES EXCHANGE ACT OF 1934, AS
AMENDED.

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               will take effect from the date of the disclaimer or such notice
               of termination and in such case the Surety will [***] pay the
               Landlord's [***] in connection with such agreement

        14.3   The insolvency of the Tenant will not affect the ability of the
               Surety under this agreement and any money received or recovered
               by the Landlord from the Surety may be placed in a separate or
               suspense account by the Landlord without any obligation on the
               Landlord to apply it in or towards the discharge of the Tenant's
               obligations under this agreement so as to preserve the Landlord's
               tights to prove in any insolvency of the Tenant in respect of the
               whole of the Tenant's indebtedness to the Landlord under this
               agreement

        14.4   The obligations of the Surety under this agreement are in
               addition to any other right or remedy of the Landlord and will
               not be discharged diminished or in any way affected by:

               14.4.1 any time or indulgence granted by the Landlord to the
                      Tenant or any neglect or forbearance of the Landlord in
                      enforcing the obligations of the Tenant under this
                      agreement

               14.4.2 any variation of this agreement or other act omission
                      matter or thing (other than a release by deed given by the
                      Landlord) by which but for this provision the obligations
                      of the Surety under this agreement would have been so
                      discharged diminished or affected

15.     DISPUTES

        Any dispute arising under this Agreement is to be resolved by means of
        the dispute resolution procedure set out in the Shared Services
        Agreement dated on or about the date of this Agreement and made between
        the Landlord and the Tenant.

16.     JURISDICTION

        16.1   This agreement will in all respects be governed by and construed
               in accordance with English law and the parties irrevocably submit
               to the exclusive jurisdiction of the English courts

        16.2   The address for service upon the Surety in England and Wales is
               [***]

17.     THIRD PARTY RIGHTS

        17.1   Nothing in this agreement is intended to confer on any person any
               tight to enforce any term of this agreement which that person
               would not have had but for the [***]

[***] - CERTAIN CONFIDENTIAL INFORMATION CONTAINED IN THIS DOCUMENT, MARKED BY
[***] HAS BEEN OMITTED AND FILED SEPARATELY WITH THE SECURITIES AND EXCHANGE
COMMISSION PURSUANT TO RULE 24B-2 OF THE SECURITIES EXCHANGE ACT OF 1934, AS
AMENDED.

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IN WITNESS whereof this agreement has been duly executed as a deed (but not
delivered until) the day and year first before written

[***] - CERTAIN CONFIDENTIAL INFORMATION CONTAINED IN THIS DOCUMENT, MARKED BY
[***] HAS BEEN OMITTED AND FILED SEPARATELY WITH THE SECURITIES AND EXCHANGE
COMMISSION PURSUANT TO RULE 24B-2 OF THE SECURITIES EXCHANGE ACT OF 1934, AS
AMENDED.

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                                    SCHEDULE

                               STANDARD CONDITIONS

        1.     Throughout the conditions references to property being sold are
               to be construed as references to the Premises

        2.     Conditions 1.4 2.2 3.4 4.2 4.3.2 4.5.2 4.5.5 5 6.3.2 6.5 6.7
               6.8.2(b) 8.2.4 8.3 and 9 do not apply

        3.     Condition 1.1.1(f) is deleted and wherever the word "contract"
               appears in the Standard Conditions (save where followed by the
               word "rate") it is replaced by the word "agreement"

        4.     In condition 1.1.1(g) the "contract rate" is [***] per annum
               above the base rate from time to time of Lloyds TSB Bank Plc

        5.     In condition 1.3.5 "5.00 pm" is substituted for "4.00 pm" and the
               words "before 5.00 pm" are added after the words "treated as
               having been received"

        6.     In condition 1.3.6 "5.00 pm" is substituted for "4.00 pm" and the
               words "(d) by fax: if sent before 5.00 pm on a working day the
               day of dispatch but otherwise on the first working day after
               dispatch" are added at the end

        7.     In condition 3.1.2 the words "(f) overriding interests (as
               defined in Section 70(l) of the Land Registration Act 1925)" are
               added at the end

        8.     In condition 4.1 the words "4.1.5 If the buyer persists in any
               valid requisition with which the seller is unable or unwilling on
               reasonable grounds to deal satisfactorily and does not withdraw
               it within five working days of being requited so to do the seller
               may by notice to the buyer and notwithstanding any intermediate
               negotiation or litigation rescind the agreement, are added at the
               end

        9.     In conditions 6.1.2 and 6.1.3 "12 noon" is substituted for "2.00
               pm"

        10.    In condition 7.1.1 the words "or in the negotiations leading to
               it" and "or was" are deleted

[***] - CERTAIN CONFIDENTIAL INFORMATION CONTAINED IN THIS DOCUMENT, MARKED BY
[***] HAS BEEN OMITTED AND FILED SEPARATELY WITH THE SECURITIES AND EXCHANGE
COMMISSION PURSUANT TO RULE 24B-2 OF THE SECURITIES EXCHANGE ACT OF 1934, AS
AMENDED.

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EXECUTED AS A DEED by EVANS            )
VACCINES LIMITED in the presence of    )

                                      Director           /s/ ALAN JARVIS

                                      Director/Secretary /s/ C.S.W. SWINGLAND

[***] - CERTAIN CONFIDENTIAL INFORMATION CONTAINED IN THIS DOCUMENT, MARKED BY
[***] HAS BEEN OMITTED AND FILED SEPARATELY WITH THE SECURITIES AND EXCHANGE
COMMISSION PURSUANT TO RULE 24B-2 OF THE SECURITIES EXCHANGE ACT OF 1934, AS
AMENDED.

                                       10
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EXECUTED AS A DEED by                  )
AVIRON UK LIMITED in the presence of   )

                                            Director           /s/ RAY PRASAD

                                            Secretary/Director /s/ FRED KURLAND

EXECUTED AS A DEED by                  )
AVIRON in the presence of              )

                                            Director           /s/ FRED KURLAND

                                            Secretary/Director /s/ RAY PRASAD

[***] - CERTAIN CONFIDENTIAL INFORMATION CONTAINED IN THIS DOCUMENT, MARKED BY
[***] HAS BEEN OMITTED AND FILED SEPARATELY WITH THE SECURITIES AND EXCHANGE
COMMISSION PURSUANT TO RULE 24B-2 OF THE SECURITIES EXCHANGE ACT OF 1934, AS
AMENDED.

                                       11

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