Theriva Biologics, Inc.

THERIVA BIOLOGICS, INC 9605 MEDICAL CENTER DRIVE, SUITE 270 ROCKVILLE, MARYLAND 20850 TO VOTE, MARK BLOCKS BELOW IN BLUE OR BLACK INK AS FOLLOWS: SCAN TO ? VIEW MATERIALS & VOTE 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. V57990-P19707 KEEP THIS PORTION FOR YOUR RECORDSTHIS PROXY CARD IS VALID ONLY WHEN SIGNED AND DATED. DETACH AND RETURN THIS PORTION ONLYTHERIVA BIOLOGICS, INC The Board of Directors recommends you vote FOR the election of each of the following: 1. Election of Directors Nominees: 01) Jeffrey J. Kraws 02) Steven A. Shallcross 03) John Monahan 04) Jeffrey Wolf, J.D. The Board of Directors recommends you vote FOR proposals 2-5: 2. To ratify the appointment of BDO USA, P.C. as our independent registered public accounting firm for our fiscal year ending on December 31, 2024. 3. To approve amendments to the Company’s 2020 Stock Incentive Plan to increase the number of shares of common stock that we will have authority to grant under the plan from 280,000 to 2,500,000 and to amend the annual non-employee director grant limit to 250,000 shares of common stock. For Withhold For All To withhold authority to vote for any individual All All Except nominee(s), mark "For All Except" and write the number(s) of the nominee(s) on the line below. 4. To approve an amendment to the Company’s Articles of Incorporation, to effect an increase to the number of authorized shares of common stock from 14,000,000 to 350,000,000, such amendment to be effected after stockholder For Against Abstain approval thereof only in the event the Board of Directors still deems it advisable.5. To approve the adjournment of 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 ofProposal 3 and/or 4. Note: To transact such other business as may properly come before the meeting or any adjournments or postponements of the meeting. For Against AbstainPlease 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 (Joint Owners) 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, 2023 are available at www.proxyvote.com. V57991-P19707 THERIVA BIOLOGICS, INC ANNUAL MEETING OF STOCKHOLDERS OCTOBER 31, 2024 AT 9:30 A.M. (Eastern 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 9:30 A.M., Eastern Time, on October 31, 2024 at the offices of the Company located at 9605 Medical Center Drive, Suite 270, Rockville, Maryland 20850, 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. Continued and to be signed on reverse side