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): July 7, 2026

THERIVA BIOLOGICS, INC.

(Exact name of registrant as specified in its charter)

9605 Medical Center Drive, Suite 270

Rockville, Maryland 20850

(Address of principal executive offices and zip code)

(301) 417-4364

Registrant’s telephone number, including area code

N/A

(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 (see General Instruction A.2. below):

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

Indicate by check mark whether the registrant is an emerging growth company as defined in in Rule 405 of the Securities Act of 1933 (17 CFR §230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (17 CFR §240.12b-2 of this chapter).

Emerging growth company ¨

If an emerging growth company, indicate by checkmark 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. ¨

Item 7.01. Regulation FD Disclosure.

On July 7, 2026, Theriva Biologics, Inc. (the “Company”) issued a press release announcing that the Spanish Agency of Medicines and Medical Devices (“AEMPS”) has authorized the Company to initiate the VIRAGE2 clinical trial, entitled ”A Phase IIa, single-arm, single-center, open-label, proof-of-concept trial evaluating increased frequency dosing of zabilugene almadenorepvec (VCN-01) in combination with gemcitabine/nab-paclitaxel in patients with newly-diagnosed metastatic pancreatic cancer” (EUCT: 2026-525566-21-00).

The VIRAGE2 trial builds on the results of the 112-patient VIRAGE Phase 2b clinical trial evaluating VCN-01 in treatment naïve metastatic pancreatic ductal adenocarcinoma (PDAC) patients receiving gemcitabine/nab-paclitaxel standard-of-care (SoC) chemotherapy. In the VIRAGE trial, patients who received 2 doses of VCN-01 administered 3 months apart had significantly improved overall survival, progression free survival, and duration of response compared to patients treated with only one dose of VCN-01 or with SoC chemotherapy alone. As previously reported, both the EMA and the FDA recognized the improved survival in the group treated with 2 doses of VCN-01, and raised the possibility of more frequent repeated dosing of VCN-01 in combination with SoC chemotherapy to potentially improve clinical outcomes. The VIRAGE2 trial is designed to evaluate the feasibility of administering at least 3 doses of VCN-01 given 2 months apart in combination with SoC chemotherapy. Results from this trial will inform the VCN-01 dosing regimen for potential evaluation in a future pivotal Phase 3 clinical trial.

The information in this Item 7.01 and in the press release furnished as Exhibit 99.1 to this Current Report on Form 8-K shall not be deemed to be “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or otherwise subject to the liabilities of that section or Sections 11 and 12(a)(2) of the Securities Act of 1933, as amended and shall not be incorporated by reference into any filing with the U.S. Securities and Exchange Commission made by the Company, whether made before or after the date hereof, regardless of any general incorporation language in such filing. The press release furnished as Exhibit 99.1 to this Current Report on Form 8-K includes “safe harbor” language pursuant to the Private Securities Litigation Reform Act of 1995, as amended, indicating that certain statements contained therein are “forward-looking” rather than historical.

Item 8.01. Other Events. 

On July 7, 2026, the Company issued a press release announcing that the AEMPS has authorized the Company to initiate the VIRAGE2 clinical trial, entitled ”A Phase IIa, single-arm, single-center, open-label, proof-of-concept trial evaluating increased frequency dosing of zabilugene almadenorepvec (VCN-01) in combination with gemcitabine/nab-paclitaxel in patients with newly-diagnosed metastatic pancreatic cancer” (EUCT: 2026-525566-21-00).

The VIRAGE2 trial builds on the results of the 112-patient VIRAGE Phase 2b clinical trial evaluating VCN-01 in treatment naïve metastatic pancreatic ductal adenocarcinoma (PDAC) patients receiving gemcitabine/nab-paclitaxel standard-of-care (SoC) chemotherapy. In the VIRAGE trial, patients who received 2 doses of VCN-01 administered 3 months apart had significantly improved overall survival, progression free survival, and duration of response compared to patients treated with only one dose of VCN-01 or with SoC chemotherapy alone. As previously reported, both the EMA and the FDA recognized the improved survival in the group treated with 2 doses of VCN-01, and raised the possibility of more frequent repeated dosing of VCN-01 in combination with SoC chemotherapy to potentially improve clinical outcomes. The VIRAGE2 trial is designed to evaluate the feasibility of administering at least 3 doses of VCN-01 given 2 months apart in combination with SoC chemotherapy. Results from this trial will inform the VCN-01 dosing regimen for potential evaluation in a future pivotal Phase 3 clinical trial.

Item 9.01. Financial Statements and Exhibits.

SIGNATURES

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.

ATTACHMENTS / EXHIBITS

EXHIBIT 99.1

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