Material Event (Form 8-K)

As previously disclosed, on May 21, 2025, Vigil Neuroscience, Inc., a Delaware corporation (the "Company" or "Vigil"), entered into an Agreement and Plan of Merger (the "Merger Agreement") with Sanofi, a French sociétéanonyme("Parent" or "Sanofi"), and Vesper Acquisition Sub Inc., a Delaware corporation and a wholly-owned subsidiary of Parent ("Merger Sub"), pursuant to which Merger Sub will merge with and into the Company (the "Merger"), with the Company surviving the Merger as a wholly-owned subsidiary of Parent.

The completion of the Merger is conditioned upon, among other things, the expiration or termination of the required waiting period applicable to the consummation of the Merger under the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended (the "HSR Waiting Period"). The HSR Waiting Period expired at 11:59 p.m., Eastern Time, on July 16, 2025.

The completion of the Merger remains subject to the satisfaction or waiver of other customary closing conditions specified in the Merger Agreement, including the adoption of the Merger Agreement by the Company's stockholders. As previously disclosed, the special stockholder meeting to consider adoption of the Merger Agreement has been scheduled to be held virtually on August 4, 2025, at 8:30 a.m., Eastern Time.