UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

Proxy Statement Pursuant to Section 14(a) of the

Securities Exchange Act of 1934 (Amendment No.          )

Filed by the Registrant              x

Filed by a Party other than the Registrant            ¨

Check the appropriate box:

¨ Preliminary Proxy Statement

¨ Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2))

¨ Definitive Proxy Statement

x Definitive Additional Materials

¨ Soliciting Material under §240.14a-12

BARINTHUS BIOTHERAPEUTICS PLC

(Name of Registrant as Specified in Its Charter)

N/A

(Name of Person(s) Filing Proxy Statement, if other than the Registrant)

Payment of Filing Fee (Check all boxes that apply):

x No fee required.

¨ Fee paid previously with preliminary materials.

¨ Fee computed on table below in exhibit required  by Item 25(b) Exchange Act Rules 14a-6(i)(14) and 0-11.

Your Vote Counts! BARINTHUS BIOTHERAPEUTICS PLC 2025 Annual Meeting Vote by June 03, 2025 11 :59 PM ET You invested in BARI NTH US BIOTHERAPEUTICS PLC and it's time to vote! You have the right to vote on proposals being presented at the Annual Meeting. This is an important notice regarding the availability of proxy material for the shareholder meeting to be held on June 10, 2025. Get informed before you vote View the Annual Report on Form 10-K, U.K. Statutory Annual Accounts and Reports, Proxy Statement on line OR you can receive a free paper or email copy of the material(s) by request ing prior to May 19, 2025. If you would like to request a copy of the material(s) for this and/or future shareholder meetings, you may (1) visit www.ProxyVote.com, (2) call 1-800-579-1639 or (3) send an email to sendmaterial@proxyvote.com. If sending an email, please include your control number (indicated below) in the subject line. Unless requested, you will not otherwise receive a paper or email copy. w For complete information and to vote, visit www.ProxyVote.com Control# ~ [!I r Point your camera here and [!I .. vote without entering a Smartphone users ~!number xxxx xxxx xxxx xxxx Vote in Person at the Meeting* June 10, 2025 9:30 AM EST Goodwin Procter (UK) LLP Sancroft, 10-15 Newgate Street London, EC1A 7AZ 2:30 PM London Time