FORM OF VOTING AND SUPPORT AGREEMENT THIS VOTING AND SUPPORT AGREEMENT (this Agreement ) is made and entered into as of [ ], 2025, by and between Sanofi, a French soci t anonyme ( Parent ), and the undersigned stockholde

FORM OF VOTING AND SUPPORT AGREEMENT

THIS VOTING AND SUPPORT AGREEMENT (this Agreement ) is made and entered into as of [ ], 2025, by and

between Sanofi, a French soci t anonyme ( Parent ), and the undersigned stockholder (the Stockholder ) of Vigil Neuroscience, Inc., a Delaware corporation (the

Company ), listed on Schedule A hereto.

WHEREAS, concurrently with the execution of this Agreement, Parent, Vesper Acquisition Sub Inc., a Delaware corporation and a wholly

owned subsidiary of Parent ( Merger Sub ), and the Company are entering into an Agreement and Plan of Merger (as amended, restated, supplemented, waived or otherwise modified from time to time, the Merger

Agreement ) that provides, among other things, Merger Sub will be merged with and into the Company (the Merger ), with the Company surviving the Merger as a wholly owned subsidiary of Parent, on the terms and

subject to the conditions set forth in the Merger Agreement and in accordance with the General Corporation Law of the State of Delaware;

WHEREAS, as of the date hereof, the Stockholder is the record and beneficial owner (as defined in Rule

13d-3 under the Exchange Act) of the number of Shares set forth opposite the Stockholder s name on Schedule A hereto (all such Shares, together with any additional Shares that are issued to or

otherwise directly or indirectly acquired or beneficially owned by the Stockholder, from and after the date hereof until the Expiration Time, collectively, the Subject Shares and such additional shares, the

After-Acquired Shares ); provided that Subject Shares shall not include Shares beneficially owned in the form of Company Warrants or Company Options, but only to the extent such Company Warrants or Company

Options remain unexercised;

WHEREAS, as of the date hereof, the Stockholder is the record and beneficial owner of the warrants and

options, as applicable, set forth opposite the Stockholder s name on Schedule A hereto (all such warrants and options, together with the Subject Shares and any additional warrants, options, convertible securities or other rights to

acquire Shares of which the Stockholder may become the record or beneficial owner from and after the date hereof until the Expiration Time, the Subject Securities ); and

WHEREAS, as a condition and inducement to the willingness of Parent and Merger Sub to enter into the Merger Agreement, the Stockholder

(solely in the Stockholder s capacity as a stockholder of the Company) has agreed to enter into this Agreement and abide by the covenants and obligations set forth herein.

NOW, THEREFORE, intending to be legally bound, the parties hereto agree as follows:

Section 1.01 All capitalized terms that are used but not defined herein shall have the respective meanings ascribed to them in the Merger

Agreement. For all purposes of and under this Agreement, the following terms shall have the following respective meanings:

Section 1.02 Adverse Amendment means an amendment or modification after the date hereof to the Merger Agreement

in the form as it exists as of the time of the execution of the Merger Agreement in a manner that decreases the amount or changes the form of consideration to be paid to the holders of Shares in the Merger or otherwise amends or modifies the Merger

Agreement in a manner materially adverse to the rights of any Stockholder (in its capacity as such) under the Merger Agreement (it being acknowledged and agreed that no increase in the amount of consideration payable to holders of Shares in the

Merger shall be adverse to any Stockholder).

Section 1.03 Expiration Time means the earliest to occur of

(a) such date and time as the Merger Agreement shall have been validly terminated pursuant to Article VII thereof, (b) the Effective Time, (c) with respect to the Stockholder, the delivery of written notice of termination by

the Stockholder to Parent following an Adverse Amendment made without the consent of the Stockholder or (d) with respect to the Stockholder, mutual written agreement of the Stockholder and Parent to terminate this Agreement.

Section 1.04 Transfer means any direct or indirect transfer, sale, assignment, pledge, encumbrance,

hypothecation, grant of a security interest in, gift, distribution or other disposal of all or any portion of the Subject Securities (or any interest in or right to such Subject Securities), whether by merger, consolidation, statutory conversion,

statutory domestication, statutory transfer, share exchange, business combination transaction, by operation of law or otherwise, including (i) any swap, derivative or other similar transaction that hedges or transfers the economic consequences

of ownership of the applicable portion of the Subject Securities or (ii) any transfer of voting rights of any portion of the Subject Shares, including by depositing any Subject Shares into a voting trust or entering into a voting agreement or

arrangement (other than this Agreement) or granting any proxy or power of attorney (other than any grant of proxy or voting instructions in a manner entirely consistent with Article III) with respect to any Subject Shares.

Section 1.05 Shares underlying Company Warrants and Company Options shall not be deemed to constitute Subject Shares until the Company

Warrants or Company Options have been exercised in accordance with their terms, at which time any Shares issued upon the exercise of such Company Warrants or Company Options shall become After-Acquired Shares and Subject

Shares for all purposes of this Agreement and shall be subject to, among other things, the requirements of Section 3.01.

TRANSFER RESTRICTIONS

Section 2.01 The Stockholder agrees that from the date hereof until the Expiration Time, the Stockholder shall not Transfer (or cause,

permit or commit to the Transfer of) any of the Subject Securities, or enter into any Contract, option, put, call or other agreement, arrangement or understanding with respect to the Transfer, except (a) transferring Subject Securities to

(i) the Stockholder s Affiliates, (ii) to any family member (including a trust for such family member s benefit) of the Stockholder or (iii) pursuant to any trust or will of the Stockholder or by the laws of intestate

succession, provided that, as a condition to such Transfer, the recipient agrees in writing to be bound by this Agreement by executing and delivering a joinder agreement in form and substance reasonably acceptable to Parent,

(b) transferring Subject Securities to any custodian or nominee solely for the purpose of holding such Subject Securities for the account of the Stockholder, or (c) with Parent s prior written consent and in Parent s sole

discretion (such exceptions set forth in sections (a) through (c), referred to as Permitted Transfers ). Any Transfer (other than a Permitted Transfer), or purported Transfer (other than a Permitted Transfer), of

Subject Securities in breach or violation of this Agreement shall be void and of no force or effect. Upon the execution and delivery of a joinder agreement pursuant to clause (i) above by a Transferee, such Transferee shall be deemed to be a

party hereto as a Stockholder as if such Transferee s signature appeared on the signature pages of this Agreement.

If any involuntary Transfer of any of such Subject Securities shall occur, the Transferee shall take and hold such Subject Securities subject to all of the restrictions, liabilities and rights under this Agreement, which shall continue in full force

and effect until valid termination of this Agreement.

AGREEMENT TO VOTE SUBJECT SHARES

Section 3.01 From the date hereof until the Expiration Time, at every meeting of the stockholders of the Company, however called, and at

every adjournment or postponement thereof, and on every action or approval by consent of the stockholders of the Company in lieu of a meeting, the Stockholder (in the Stockholder s capacity as such) agrees to appear and be present at each such

meeting (in person or by proxy) or otherwise cause all of the Stockholder s Subject Shares to be counted as present thereat for purpose of determining a quorum, and, unconditionally and irrevocably, to vote, or to direct the holder of record on

any applicable record date to vote (or, in the case of an action by consent of stockholders in lieu of a meeting, to deliver a consent (or cause a consent to be delivered)) in respect of all Subject Shares that are then-owned by the Stockholder and

(a) in favor of (i) the adoption of the Merger Agreement, the Merger and the approval of all agreements related to

the Merger and any actions related thereto; (ii) without limitation of the preceding clause (i), the approval of any proposal to adjourn or postpone any such meeting to a later date if there are not sufficient votes for adoption of the Merger

Agreement on the date on which such meeting is held and (iii) each of the transactions contemplated by the Merger Agreement;

(b) against approval of any proposal made in opposition to, in competition with, or

inconsistent with, the Merger Agreement, the Merger or any other transactions contemplated by the Merger Agreement;

the following actions (other than those actions that relate to the approval of the Merger or any other transactions contemplated by the Merger Agreement): (A) any merger, consolidation, statutory conversion, statutory domestication, statutory

transfer, share exchange, business combination, sale of assets, reorganization or recapitalization of or involving the Company or any of its subsidiaries, (B) any sale, lease, exchange, transfer or other disposition of a material amount of the

assets of the Company or any of its subsidiaries, (C) any reorganization, recapitalization, dissolution, liquidation or winding up of the Company or any of its subsidiaries, (D) any material change in the capitalization of the Company or

any of its subsidiaries, or the corporate structure of the Company or any of its subsidiaries or any amendment, modification, supplement or other change in the Company s organizational documents, (E) any Acquisition Proposal or

(F) any other action, proposal, transaction or agreement that would reasonably be expected to materially prevent, nullify, impede, interfere with, delay, postpone, frustrate, discourage or adversely affect the Merger or any other transactions

contemplated by the Merger Agreement;

(d) against any action, proposal, transaction or agreement that would reasonably be expected to

result in a breach in any respect of any covenant, representation or warranty or any other obligation or agreement of the Company contained in the Merger Agreement, or of the Stockholder contained in this Agreement; and

(e) in favor of any other matter necessary or appropriate to the consummation of the transactions contemplated by the Merger Agreement,

including the Merger.

Section 3.02 The Stockholder hereby revokes (or agrees to cause to be revoked) any proxies or grants of power

of attorney that it has heretofore granted with respect to the Subject Shares.

Section 3.03 The Stockholder shall not enter into any

agreement, arrangement or understanding with any Person to vote, provide consent or give instructions in any manner inconsistent with the terms of this Article III.

From the date hereof until the Expiration Time, the Stockholder shall, and shall direct its Representatives to, cease any direct or

indirect solicitation, encouragement, discussions or negotiations with any Persons that may be ongoing with respect to an Acquisition Proposal, and the Stockholder shall not and shall direct such Representatives not to, take any action that the

Company would then be prohibited from taking under Section 4.3 of the Merger Agreement as if the Stockholder were the Company. Notwithstanding anything to the contrary provided in this

Agreement, the Stockholder and any of its Representatives shall not be prohibited from participating in any discussions or negotiations with respect to a possible voting and support, voting or

similar agreement in connection with an Acquisition Proposal in the event that the Company is permitted to take the actions set forth in Section 4.3(c) of the Merger Agreement with respect to such Acquisition Proposal.

REPRESENTATIONS AND WARRANTIES OF THE STOCKHOLDERS

The Stockholder hereby represents and warrants to Parent as follows:

Section 5.01 Power; Organization; Binding Agreement. The Stockholder has full power and authority (or capacity, in the case of

Stockholders that are natural persons) to execute and deliver and perform the Stockholder s obligations under this Agreement and to consummate the transactions contemplated hereby. In the case of a Stockholder that is not a natural person, the

Stockholder is duly organized, validly existing and in good standing under the laws of its jurisdiction of organization (except to the extent the good standing concept is not applicable in any relevant jurisdiction) and the execution and

delivery of this Agreement and the Stockholder s performance of its obligations under this Agreement have been duly authorized by all necessary corporate or similar action on the part of the Stockholder and no other corporate or similar

proceedings on the part of the Stockholder are necessary to authorize the execution and delivery of this Agreement or for the Stockholder to perform its obligations under this Agreement. This Agreement has been duly executed and delivered by the

Stockholder, and, assuming this Agreement constitutes a valid and binding obligation of Parent, constitutes a valid and binding obligation of the Stockholder, enforceable against the Stockholder in accordance with its terms, subject to the

Enforceability Exceptions.

Section 5.02 No Conflicts. None of the execution and delivery by the Stockholder of this

Agreement, the performance by the Stockholder of its obligations hereunder or the consummation by the Stockholder of the transactions contemplated hereby will (i) conflict with, result in a breach by the Stockholder of, constitute a default

(with or without notice or lapse of time, or both) on the part of the Stockholder under, or require any Consent under, or give rise to a right of termination, cancellation, first offer, first refusal, modification, or acceleration of any obligation

or loss of any benefit under, any Contract, including any voting agreement or voting trust, (ii) cause a violation by the Stockholder of any Legal Requirement or Order applicable to the Stockholder, or to which they are subject, or

(iii) cause a violation of any of the provisions of the certificate of incorporation or bylaws or other organizational documents of the Stockholder, in the case of Stockholders that are not natural persons, except, in the case of the preceding

clauses (i) and (ii), as would not prevent or materially delay the Stockholder from performing the Stockholder s obligations under this Agreement.

Section 5.03 Ownership of Shares. The Stockholder (i) is the sole owner of the Subject Shares and the Subject Securities set

forth on Schedule A to this Agreement, all of which are free and clear of any Encumbrances (except any lien arising under securities laws or arising hereunder) and (ii) except as set forth on Schedule A to this Agreement, does not

own (beneficially, of record or otherwise), any other Shares or other securities, interests, warrants, options or other rights to purchase or subscribe for or otherwise acquire any Shares and has no interest in or voting rights with respect to any

securities of the Company.

Section 5.04 Voting Power. The Stockholder has sole voting power, sole power of

disposition, sole power to issue instructions with respect to the matters set forth herein, and sole power to agree to all of the matters set forth in this Agreement, in each case with respect to all of the Subject Shares, with no limitations,

qualifications or restrictions on such rights, subject to applicable federal securities laws and arising under the terms of this Agreement. Except for this Agreement, the Stockholder has not (i) entered into any voting agreement, voting trust

or similar agreement or understanding with respect to any of the Subject Shares, (ii) deposited any of the Subject Shares in any voting trust or (iii) granted any proxy, consent or power of attorney, voting instructions or authorities with

respect to any of the Subject Shares in any manner inconsistent with the terms of Article III.