Abivax to Join CAC Mid 60 and SBF 120 Indices Following Euronext Paris Annual Review

PARIS, France, September 12, 2025, 5:45 p.m. CEST – Abivax SA (PARIS:FR) ("Abivax" or the "Company"), a clinical-stage biotechnology company focused on developing therapeutics that harness the body's natural regulatory mechanisms to modulate the inflammatory response in patients with chronic inflammatory diseases, announces today that following the annual review of the Euronext Paris indices on September 11, 2025, the Scientific Council of the Indices has decided to admit Abivax to the CAC Mid 60 and SBF 120 indices.

This decision will take effect on Friday, September 19, 2025, after market close.

The CAC Mid 60 and SBF 120 are key indices on the Euronext Paris exchange, representing mid-sized listed companies and a broader selection of 120 major securities, respectively. Inclusion in these indices enhances Abivax's visibility and is expected to broaden the Company's investor base by making its shares more accessible to institutional investors and index-linked funds.

"We are honored to be added to the Euronext CAC Mid 60 and SBF 120 indices," said Marc de Garidel, Chief Executive Officer of Abivax. "This recognition is a powerful testament to the financial markets' continued confidence in our strategic visions and our ability to execute them. This milestone also further validates our commitment to advancing innovative therapies for patients with chronic inflammatory diseases while driving long-term value for our shareholders."

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About Abivax

Abivax is a clinical-stage biotechnology company focused on developing therapeutics that harness the body's natural regulatory mechanisms to stabilize the immune response in patients with chronic inflammatory diseases. Based in France and the United States, Abivax's lead drug candidate, obefazimod (ABX464), is in Phase 3 clinical trials for the treatment of moderately to severely active ulcerative colitis. More information on the Company is available at www.abivax.com. Follow us on LinkedIn and on X, formerly Twitter, @ABIVAX.

Contacts:

Abivax Investor Relations

Patrick Malloy

patrick.malloy@abivax.com

+1 847 987 4878

FORWARD-LOOKING STATEMENTS

This press release contains forward-looking statements, forecasts and estimates, including those relating to the Company's business and financial objectives. Words such as "design," "expect," "forward," "future," "potential," "plan," "project," "will" and variations of such words and similar expressions are intended to identify forward-looking statements. These forward-looking statements include statements concerning or implying the therapeutic potential of Abivax's drug candidates, the potential benefits of Abivax being admitted to the CAC Mid 60 and SBF 120 indices, and other statements that are not historical fact. Although Abivax's management believes that the expectations reflected in such forward-looking statements are reasonable, investors are cautioned that forward-looking information and statements are subject to various risks, contingencies and uncertainties, many of which are difficult to predict and generally beyond the control of Abivax, that could cause actual results and developments to differ materially from those expressed in, or implied or projected by, the forward-looking information and statements. A description of these risks, contingencies and uncertainties can be found in the documents filed by the Company with the French Autorité des Marchés Financiers pursuant to its legal obligations including its universal registration document (Document d'Enregistrement Universel) and in its Annual Report on Form 20-F filed with the U.S. Securities and Exchange Commission on March 24, 2025 under the caption "Risk Factors." These risks, contingencies and uncertainties include among other things, the uncertainties inherent in research and development, future clinical data and analysis, decisions by regulatory authorities, such as the FDA or the EMA, regarding whether and when to approve any drug candidate, as well as their decisions regarding labelling and other matters that could affect the availability or commercial potential of such product candidates. and the availability of funding sufficient for the Company's foreseeable and unforeseeable operating expenses and capital expenditure requirements. Special consideration should be given to the potential hurdles of clinical and pharmaceutical development including further assessment by the Company and regulatory agencies and IRBs/ethics committees following the assessment of preclinical, pharmacokinetic, carcinogenicity, toxicity, CMC and clinical data. Furthermore, these forward-looking statements, forecasts and estimates are made only as of the date of this press release. Readers are cautioned not to place undue reliance on these forward-looking statements. Abivax disclaims any obligation to update these forward-looking statements, forecasts or estimates to reflect any subsequent changes that the Company becomes aware of, except as required by law. Information about pharmaceutical products (including products currently in development) that is included in this press release is not intended to constitute an advertisement. This press release is for information purposes only, and the information contained herein does not constitute either an offer to sell, or the solicitation of an offer to purchase or subscribe securities of the Company in any jurisdiction. Similarly, it does not give and should not be treated as giving investment advice. It has no connection with the investment objectives, financial situation or specific needs of any recipient. It should not be regarded by recipients as a substitute for exercise of their own judgment. All opinions expressed herein are subject to change without notice. The distribution of this document may be restricted by law in certain jurisdictions. Persons into whose possession this document comes are required to inform themselves about and to observe any such restrictions.