Form DEFA14A SOLIGENIX, INC.

Your Vote Counts! Smartphone users Point your camera here and vote without entering a control number For complete information and to vote, visit www.ProxyVote.com Control # T02408-P55983 SOLIGENIX, INC. 29 EMMONS DRIVE SUITE B-10 PRINCETON, NJ 08540 SOLIGENIX, INC. 2026 Annual Meeting Vote by September 16, 2026 11:59 PM ET You invested in SOLIGENIX, INC. 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 materials for the stockholder meeting to be held on September 17, 2026. Vote Virtually at the Meeting* September 17, 2026 9:00 a.m., Eastern Daylight Time Virtually at: www.virtualshareholdermeeting.com/SNGX2026 *Please check the meeting materials for any special requirements for meeting attendance. Get informed before you vote View the Notice and Proxy Statement and Form 10-K online OR you can receive a free paper or email copy of the material(s) by requesting prior to September 3, 2026. If you would like to request a copy of the material(s) for this and/or future stockholder meetings, you may (1) visit www.ProxyVote.com, (2) call 1-800-579-1639 or (3) send an email to [email protected]. 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.

Vote at www.ProxyVote.com Prefer to receive an email instead? While voting on www.ProxyVote.com, be sure to click “Delivery Settings”. Voting Items Board Recommends T02409-P55983 THIS IS NOT A VOTABLE BALLOT This is an overview of the proposals being presented at the upcoming stockholder meeting. Please follow the instructions on the reverse side to vote these important matters. 1. To elect five directors to serve until the next Annual Meeting of Stockholders or until their respective successors have been duly elected and qualified. For All Nominees: 01) Christopher J. Schaber, Ph.D. 02) Gregg A. Lapointe, C.P.A. 03) Diane L. Parks, M.B.A. 04) Robert J. Rubin, M.D. 05) Jerome B. Zeldis, M.D., Ph.D. 2. To approve an amendment to our Second Amended and Restated Certificate of Incorporation, to, at the discretion of the Board of Directors exercisable for a period of up to one year, effect a reverse stock split with respect to the issued and outstanding common stock at a ratio of 1-for-2 to 1-for-20, with the ratio to be determined at the discretion of the Board of Directors and included in a public announcement. For 3. To approve an amendment to our Second Amended and Restated Certificate of Incorporation, to increase the number of authorized shares of common stock from 75,000,000 to 125,000,000. For 4. To hold an advisory vote on executive compensation. For 5. To hold an advisory vote on the frequency of holding an advisory vote on executive compensation. 1 Year 6. To ratify the appointment of Cherry Bekaert LLP as our independent registered public accounting firm for the year ending December 31, 2026. For 7. To approve an adjournment of the Annual Meeting, in whole or in part as to any particular proposal(s), to a later date or dates, if necessary, to permit further solicitation of proxies in the event there are not sufficient shares voted to constitute a quorum or votes in favor of a particular proposal for approval. For Note: To transact such other business as may properly come before the Annual Meeting or any adjournment or postponement thereof.