Theriva Biologics, Inc.

Appendix B

CERTIFICATE OF AMENDMENT

AUTHORIZED INCREASE

FRANCISCO V. AGUILAR Secretary of State 401 North Carson Street Carson City, Nevada 89701-4201 (775) 684-5708 Website: www.nvsos.gov Profit Corporation: Certificate of Amendment (PURSUANT TO NRS 78.380 & 78.385/78.390) Certificate to Accompany Restated Articles or Amended and Restated Articles (PURSUANT TO NRS 78.403) Officer's Statement (PURSUANT TO NRS 80.030) TYPE OR PRINT - USE DARK INK ONLY - DO NOT HIGHLIGHT Page 1 of 2 Revised: 9/1/2023 1. Entity information: Name of entity as on file with the Nevada Secretary of State: This form must be accompanied by appropriate fees. Certificate to Accompany Restated Articles or Amended and Restated Articles Certificate of Amendment to Articles of Incorporation (Pursuant to NRS 78.385 and 78.390 - After Issuance of Stock) The vote by which the stockholders holding shares in the corporation entitling them to exercise at least a majority of the voting power, or such greater proportion of the voting power as may be required in the case of a vote by classes or series, or as may be required by the provisions of the articles of incorporation* have voted in favor of the amendment is: Certificate of Amendment to Articles of Incorporation (Pursuant to NRS 78.380 - Before Issuance of Stock) The undersigned declare that they constitute at least two-thirds of the following: (Check only one box) incorporators board of directors The undersigned affirmatively declare that to the date of this certificate, no stock of the corporation has been issued Officer's Statement (foreign qualified entities only) - Name in home state, if using a modified name in Nevada: Jurisdiction of formation: Changes to takes the following effect: The entity name has been amended. The purpose of the entity has been amended. The authorized shares have been amended. Other: (specify changes) * Officer's Statement must be submitted with either a certified copy of or a certificate evidencing the filing of any document, amendatory or otherwise, relating to the original articles in the place of the corporations creation. Dissolution Merger Conversion 3. Type of Amendment Filing Being Completed: (Select only one box) (If amending, complete section 1, 3, 5 and 6.) 2. Restated or Amended and Restated Articles: (Select one) (If amending and restating only, complete section 1,2 3, 5 and 6) Amended and Restated Articles * Restated or Amended and Restated Articles must be included with this filing type. Entity or Nevada Business Identification Number (NVID): Restated Articles - No amendments; articles are restated only and are signed by an officer of the corporation who has been authorized to execute the certificate by resolution of the board of directors adopted on: The certificate correctly sets forth the text of the articles or certificate as amended to the date of the certificate. Or No action by stockholders is required, name change only.

FRANCISCO V. AGUILAR Secretary of State 401 North Carson Street Carson City, Nevada 89701-4201 (775) 684-5708 Website: www.nvsos.gov Profit Corporation: Certificate of Amendment (PURSUANT TO NRS 78.380 & 78.385/78.390) Certificate to Accompany Restated Articles or Amended and Restated Articles (PURSUANT TO NRS 78.403) Officer's Statement (PURSUANT TO NRS 80.030) 4. Effective Date and Date: Time: Time: (Optional) (must not be later than 90 days after the certificate is filed) 5. Information Being Changes to takes the following effect: Changed: (Domestic The entity name has been amended. corporations only) The registered agent has been changed. (attach Certificate of Acceptance from new registered agent) The purpose of the entity has been amended. The authorized shares have been amended. The directors, managers or general partners have been amended. IRS tax language has been added. Articles have been added. Articles have been deleted. Other. The articles have been amended as follows: (provide article numbers, if available) (attach additional page(s) if necessary) 6. Signature: (Required) X ____________________________ Signature of Officer or Authorized Signer Title X ____________________________ Signature of Officer or Authorized Signer Title *If any proposed amendment would alter or change any preference or any relative or other right given to any class or series of outstanding shares, then the amendment must be approved by the vote, in addition to the affirmative vote otherwise required, of the holders of shares representing a majority of the voting power of each class or series affected by the amendment regardless to limitations or restrictions on the voting power thereof. Please include any required or optional information in space below: (attach additional page(s) if necessary) This form must be accompanied by appropriate fees. Page 2 of 2 Revised: 9/1/2023

Theriva Biologics, Inc. 9605 Medical Center, Suite 270 Rockville, Maryland 20850 VOTE BY INTERNET - www.proxyvote.com or scan the QR Barcode above Use the Internet to transmit your voting instructions and for electronic delivery of information up until 11:59 p.m. Eastern Time the day before the meeting date. Have your proxy card in hand when you access the web site and follow the instructions to obtain your records and to create an electronic voting instruction form. ELECTRONIC DELIVERY OF FUTURE PROXY MATERIALS - If you would like to reduce the costs incurred by our company in mailing proxy materials, you can consent to receiving all future proxy statements, proxy cards and annual reports electronically via e-mail or the Internet. To sign up for electronic delivery, please follow the instructions above to vote using the Internet and, when prompted, indicate that you agree to receive or access proxy materials electronically in future years. VOTE BY PHONE - 1-800-690-6903 Use any touch-tone telephone to transmit your voting instructions up until 11:59 p.m. Eastern Time the day before the meeting date. Have your proxy card in hand when you call and then follow the instructions. VOTE BY MAIL Mark, sign and date your proxy card and return it in the postage-paid envelope we have provided or return it to Vote Processing, c/o Broadridge, 51 Mercedes Way, Edgewood, NY 11717. TO VOTE, MARK BLOCK BELOW IN BLUE OR BLACK INK AS FOLLOWS: KEEP THIS PORTION FOR YOUR RECORDS DETACH AND RETURN THIS PORTION ONLY THIS PROXY CARD IS VALID ONLY WHEN SIGNED AND DATED. THE BOARD RECOMMENDS A VOTE “FOR” ALL NOMINEES ON PROPOSAL 1 AND “FOR” PROPOSALS 2, 3, 4, 5 AND 6. 1. Election Of Directors. FOR ALL WITHOLD ALL FOR ALL EXCEPT Jeffrey Kraws ☐ ☐ ☐ John Monahan ☐ ☐ ☐ Steven A. Shallcross ☐ ☐ ☐ Jeffrey Wolf ☐ ☐ ☐ 2. To ratify the appointment of BDO USA, P.C. as the Company’s independent registered public accounting firm for the year ending December 31, 2026 (the “Auditor Ratification Proposal”). FOR AGAINST ABSTAIN ☐ ☐ ☐ 3. To approve an amendment to the Company’s 2020 Stock Incentive Plan (the “Plan”) to increase the number of shares of the Company’s common stock, par value $0.001 per share (“Common Stock”) that it will have authority to grant under the plan to [6,500,000] shares of Common Stock (the “Plan Increase Proposal”). ☐ ☐ ☐ 4. To approve an amendment to the Company’s Articles of Incorporation, as amended (the “Articles of Incorporation”), to, at the discretion of the Board, effect an increase the number of authorized shares of Common Stock to 450,000,000 shares (the “Authorized Common Stock Increase Proposal”), such amendment to be effected after stockholder approval thereof only in the event the Board still deems it advisable. ☐ ☐ ☐ 5. To approve, pursuant to Section 713(a) of the NYSE American Company Guide and the terms of an inducement agreement, the issuance of up to an aggregate of 16,184,560 shares of Common Stock upon the exercise of the Company’s common stock purchase warrants issued to institutional investors in the Company’s private placement offering, which closed on October 17, 2025 (the “Warrant Exercise Proposal”). ☐ ☐ ☐ 6. To approve a proposal to adjourn the Annual Meeting to a later date, if necessary or appropriate, to permit further solicitation and vote of proxies in the event that there are insufficient votes for, or otherwise in connection with, the approval of the Plan Increase Proposal, the Authorized Common Stock Increase Proposal, the Reverse Stock Split Proposal and/or the Warrant Exercise Proposal (the “Adjournment Proposal”). ☐ ☐ ☐ The undersigned acknowledges receipt of our 2025 Annual Report to Stockholders, Notice of Annual Meeting of Stockholders and the Proxy Statement related thereto. Please sign exactly as your name(s) appear(s) hereon. When signing as attorney, executor, administrator, or other fiduciary, please give full title as such. Joint owners should each sign

personally. All holders must sign. If a corporation or partnership, please sign in full corporate or partnership name by authorized officer. _______________________________________ Signature Date ______________________________________ Signature (Joint Owners) Date Important Notice Regarding the Availability of Proxy Materials for the Annual Meeting: The Notice and Proxy Statement and Annual Report are available at www.proxyvote.com NOTE: To transact such other business as may properly come before the meeting or any adjournments or postponements of the meeting. Please sign exactly as your name(s) appear(s) hereon. When signing as attorney, executor, administrator, or other fiduciary, please give full title as such. Joint owners should each sign personally. All holders must sign. If a corporation or partnership, please sign in full corporate or partnership name, by authorized officer. Signature [PLEASE SIGN WITHIN BOX] Date Signature Date Important Notice Regarding the Availability of Proxy Materials for the Annual Meeting: The Notice and Proxy Statement and our Annual Report on Form 10-K for the year ended December 31, 2025 are available at www.proxyvote.com THERIVA BIOLOGICS, INC. ANNUAL MEETING OF STOCKHOLDERS AUGUST 3, 2026 AT: 3:30 P.M. (LOCAL TIME) THIS PROXY IS SOLICITED ON BEHALF OF THE BOARD OF DIRECTORS The undersigned stockholder hereby appoints Steven A. Shallcross as proxy, with the power to appoint his substitute, and hereby authorizes him to represent and to vote, as designated on the reverse side of this ballot, all of the shares of common stock of THERIVA BIOLOGICS, INC. that the undersigned is entitled to vote at the Annual Meeting of Stockholders to be held at 3:30 p.m. (local time), on August 3, 2026 at the Company’s principal place of business for research and clinical development, located at Carrer Torrent de Can Ninou, naus 5-6, 08150 - Parets del Vallès (Barcelona) Spain, or any adjournment or postponement thereof. This proxy, when properly executed, will be voted in the manner directed herein. If no such direction is made, this proxy will be voted in accordance with the Board of Directors’ recommendations.