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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): March 13, 2026

BARINTHUS BIOTHERAPEUTICS PLC

(Exact name of registrant as specified in its charter)

England and Wales001-40367Not Applicable (State or other jurisdiction of incorporation)(Commission File Number)(I.R.S. Employer Identification No.)

Barinthus Biotherapeutics plc 20400 Century Blvd, Suite 210, Germantown, MD 20874

(Address of principal executive offices, including zip code) 443 917-0966 (Registrant’s telephone number, including area code)

Not Applicable (Former name or former address, if changed since last report) Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

☒Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

oSoliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

oPre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

oPre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act:

Title of each classTrade Symbol(s)Name of each exchange on which registered

American Depositary SharesBRNSThe Nasdaq Global Market Ordinary shares, nominal value £0.000025 per share*

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter). Emerging growth company x If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. o *American Depositary Shares may be evidenced by American Depositary Receipts. Each American Depositary Share represents one (1) ordinary share. Not for trading, but only in connection with the listing of the American Depositary Shares on The Nasdaq Global Market. The American Depositary Shares represent the right to receive ordinary shares and are being registered under the Securities Act of 1933, as amended, pursuant to a separate Registration Statement on Form F-6. Accordingly, the American Depositary Shares are exempt from the operation of Section 12(a) of the Securities Exchange Act of 1934, as amended, pursuant to Rule 12a-8.

Item 2.02. Results of Operations and Financial Condition. On March 13, 2026, Barinthus Biotherapeutics plc (the “Company”) provided an overview of the Company’s progress and announced its financial results for the year ended December 31, 2025. The full text of the press release issued in connection with the update is furnished as Exhibit 99.1 to this Current Report on Form 8-K. The information in Item 2.02 of this Form 8-K (including Exhibit 99.1) shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended (the "Securities Act"), or the Exchange Act, except as expressly set forth by specific reference in such a filing.

Item 7.01 Regulation FD Disclosure.

On March 13, 2026, the Company updated its corporate presentation for use in meetings with investors, analysts and others. A copy of this presentation is furnished as Exhibit 99.2 to this Current Report on Form 8-K. The Company undertakes no obligation to update, supplement or amend the presentation.

The information in Item 7.01 of this Current Report on Form 8-K (including Exhibit 99.2) is being furnished and shall not be deemed “filed” for purposes of Section 18 of the Exchange Act, or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference into any filing by the Company under the Securities Act or the Exchange Act, except as expressly set forth by specific reference in such filing.

Additional Information and Where to Find It

In connection with the proposed transaction, the combined company plans to file with the Securities and Exchange Commission (the “SEC”) and mail or otherwise provide to Company’s investors and security holders a registration statement on Form S-4 that will contain a joint proxy statement/prospectus (the “Registration Statement”). THE COMPANY’S INVESTORS AND SECURITY HOLDERS ARE URGED TO CAREFULLY REA

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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): November 7, 2025

BARINTHUS BIOTHERAPEUTICS PLC

(Exact name of registrant as specified in its charter)

England and Wales001-40367Not Applicable (State or other jurisdiction of incorporation)(Commission File Number)(I.R.S. Employer Identification No.)

Barinthus Biotherapeutics plc 20400 Century Blvd, Suite 210, Germantown, MD 20874

(Address of principal executive offices, including zip code) 443 917-0966 (Registrant’s telephone number, including area code)

Not Applicable (Former name or former address, if changed since last report) Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

☒Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

oSoliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

oPre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

oPre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act:

Title of each classTrade Symbol(s)Name of each exchange on which registered

American Depositary SharesBRNSThe Nasdaq Global Market Ordinary shares, nominal value £0.000025 per share*

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter). Emerging growth company x If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. o *American Depositary Shares may be evidenced by American Depositary Receipts. Each American Depositary Share represents one (1) ordinary share. Not for trading, but only in connection with the listing of the American Depositary Shares on The Nasdaq Global Market. The American Depositary Shares represent the right to receive ordinary shares and are being registered under the Securities Act of 1933, as amended, pursuant to a separate Registration Statement on Form F-6. Accordingly, the American Depositary Shares are exempt from the operation of Section 12(a) of the Securities Exchange Act of 1934, as amended, pursuant to Rule 12a-8.

Item 2.02. Results of Operations and Financial Condition. On November 7, 2025, Barinthus Biotherapeutics plc (the “Company”) provided an overview of the Company’s progress and announced its financial results for the quarter ended September 30, 2025. The full text of the press release issued in connection with the update is furnished as Exhibit 99.1 to this Current Report on Form 8-K. The information in Item 2.02 of this Form 8-K (including Exhibit 99.1) shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended (the "Securities Act"), or the Exchange Act, except as expressly set forth by specific reference in such a filing. Additional Information and Where to Find It

In connection with the proposed transaction, the combined company plans to file with the Securities and Exchange Commission (the “SEC”) and mail or otherwise provide to Company’s investors and security holders a registration statement on Form S-4 that will contain a joint proxy statement/prospectus (the “Registration Statement”). THE COMPANY’S INVESTORS AND SECURITY HOLDERS ARE URGED TO CAREFULLY READ THE REGISTRATION STATEMENT IN ITS ENTIRETY WHEN IT BECOMES AVAILABLE AND ANY OTHER DOCUMENTS FILED BY THE COMPANY WITH THE SEC IN CONNECTION WITH THE PROPOSED TRANSACTION OR INCORPORATED BY REFERENCE THEREIN BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION ABOUT THE PROPOSED TRANSACTION AND THE PARTIES TO THE PROPOSED TRANSACTION.

Investors and security holders may obtain a free copy of the Registration Statement and other documents that the combined company files with the SEC (when available) from the SEC’s website at www.sec.gov or at investors.barinthusbio.com.

Participants in the Solicitation

Clywedog Therapeutics Inc. (“Clywedog”), the Company and their respective directors, executive officers, other members of management, certain employees and other per

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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K/A

(Amendment No. 1)

CURRENT REPORT

Pursuant to Section 13 or 15(d)

of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): August 7, 2025

BARINTHUS BIOTHERAPEUTICS PLC

(Exact name of registrant as specified in its charter)

England and Wales 001-40367 Not Applicable

(State or other jurisdiction

of incorporation)

(Commission

File Number)

(I.R.S. Employer

Identification No.)

Barinthus Biotherapeutics plc

20400 Century Blvd, Suite 210

Germantown,

MD 20874

(Address of principal executive offices, including zip code)

(443) 917-0966

(Registrant’s telephone number, including area code)

Not Applicable

(Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

¨ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

¨ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

¨ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

¨ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act:

Title of each class Trade Symbol(s) Name of each exchange on which

registered

American Depositary Shares

BRNS

The Nasdaq Global Market

Ordinary shares, nominal value £0.000025 per share*

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter).

Emerging growth company  x

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.  ¨

*American Depositary Shares may be evidenced by American Depositary Receipts. Each American Depositary Share represents one (1) ordinary share. Not for trading, but only in connection with the listing of the American Depositary Shares on The Nasdaq Global Market. The American Depositary Shares represent the right to receive ordinary shares and are being registered under the Securities Act of 1933, as amended, pursuant to a separate Registration Statement on Form F-6. Accordingly, the American Depositary Shares are exempt from the operation of Section 12(a) of the Securities Exchange Act of 1934, as amended, pursuant to Rule 12a-8.

00-0000000

EXPLANATORY NOTE

Barinthus Biotherapeutics plc (the “Company”) is filing this Amendment No. 1 on Form 8-K/A (this “Amendment”) to amend its Current Report on Form 8-K furnished by the Company to the Securities and Exchange Commission (the “SEC”) on August 7, 2025 (the “Original Report”). The Exhibit 99.1 to the Original Report inadvertently included an inaccurate statement in a sub-bullet describing the trial result of the Company’s Phase 1 trial of VTP-850 in patients with prostate cancer. The sole purpose of this Amendment No is to correct the information in this sub-bullet in the Exhibit 99.1. No other changes have been made to the Original Report.

Item 2.02. Results of Operations and Financial Condition.

On August 7, 2025, Barinthus Biotherapeutics plc (the “Company”) provided an overview of the Company’s progress and announced its financial results for the quarter ended June 30, 2025. The full text of the press release issued in connection with the update is furnished as Exhibit 99.1 to this Current Report on Form 8-K.

The information in Item 2.02 of this Form 8-K (including Exhibit 99.1) shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended (the "Securities Act"), or the Exchange Act, except as expressly set forth by specific reference in such a filing.

Item 9.01. Financial Statements and Exhibits.

(d)Exhibits

99.1 Press Release dated August 7, 2025.

104 Cover Page Interactive Data File (embedded within the Inline XBRL document).

SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Barinthus Biotherapeutics plc

Date: August 8, 20