Divakar Gupta +1 212 479-6474 dgupta@cooley.com		Exhibit 5.2

June 30, 2026

Abivax SA

7-11 boulevard Haussmann

75009 Paris, France

Ladies and Gentlemen:

We have acted as special U.S. counsel to Abivax SA, a société anonyme incorporated under the laws of the French Republic (the “Company”), in connection with the filing by the Company of a Registration Statement on Form F-3 (the “Registration Statement”) with the Securities and Exchange Commission (the “Commission”) under the Securities Act of 1933, as amended (the “Securities Act”). The Registration Statement includes a prospectus (the “Base Prospectus”) that provides it will be supplemented in the future by one or more prospectus supplements (each, a “Prospectus Supplement”). The Registration Statement including the Base Prospectus (as supplemented from time to time by one or more Prospectus Supplements), will provide for the registration by the Company of the sale of the following securities:

 

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ordinary shares, nominal value €0.01 per share (the “Ordinary Shares”), including Ordinary Shares represented by American Depositary Shares (the “ADSs”);

 

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debt securities, in one or more series (the “Debt Securities”), which may be issued pursuant to an indenture to be dated on or about the date of the first issuance of Debt Securities thereunder, by and between a trustee to be selected by the Company (the “Trustee”) and the Company in the form filed as Exhibit 4.4 to the Registration Statement and one or more indentures supplemental thereto with respect to any particular series of Debt Securities (the “Indenture”); and

 

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warrants to purchase Ordinary Shares, ADSs, or Debt Securities (the “Warrants”), which may be issued under any separate warrant agreement to be entered into between the Company and one or more purchasers of such warrants (the “Warrant Agreement”).

The Ordinary Shares, the Debt Securities and the Warrants are collectively referred to herein as the “Securities.” The Securities are being registered for offer and sale from time to time pursuant to Rule 415 under the Securities Act.

In rendering this opinion, we have examined and relied upon the Registration Statement, the Base Prospectus and such other records, documents, certificates, opinions, memoranda and instruments as in our judgment are necessary or appropriate to enable us to render the opinion expressed below. We have assumed the genuineness of all signatures; the authenticity of all documents submitted to us as originals; the conformity to originals of all documents submitted to us as copies; the accuracy, completeness and authenticity of certificates of public officials; and the due authorization, execution and delivery of all documents. As to certain factual matters, we have relied upon a certificate of an officer of the Company and have not independently verified such matters. We are not hereby rendering any opinion with respect to any Ordinary Shares issuable upon the conversion or exercise, as applicable, of any Debt Securities or any Warrants.

Abivax SA

June 30, 2026

Page 2

 

We have assumed that (i) the Company is validly existing under the laws of the French Republic, has the corporate power to enter into and perform its obligations under the Debt Securities, the Indenture and the Warrants in accordance with their terms, (ii) upon issuance, the Company will have duly authorized, executed and delivered the Debt Securities, the Indenture and the Warrants in accordance with its organizational documents and the laws of the French Republic, (iii) any Ordinary Shares issued upon conversion of the Debt Securities, or upon exercise of Warrants will be duly authorized, validly issued, fully paid and nonassessable, and (iv) the execution and delivery, and performance by the Company of its obligations under the Debt Securities, the Indenture and the Warrants will not violate the laws of the French Republic or any other applicable laws (excepting from such assumption the laws of the State of New York). We have also assumed that any Debt Securities offered under the Registration Statement and the related Indenture will be executed in the forms filed as exhibits to the Registration Statement.

Our opinion herein is expressed solely with respect to the laws of the State of New York. Our opinion is based on these laws as in effect on the date hereof. We express no opinion to the extent that any other laws are applicable to the subject matter hereof and express no opinion and provide no assurance as to compliance with any federal or state securities law, rule or regulation.

On the basis of the foregoing, in reliance thereon, and subject to the assumptions, qualifications, limitations and exceptions set forth herein, we are of the opinion that:

1. With respect to any series of Debt Securities issued under the Indenture and offered under the Registration Statement, provided that: (i) the Registration Statement and any required post-effective amendment thereto have become effective under the Securities Act and the Base Prospectus and any and all Prospectus Supplement(s) required by applicable laws have been delivered and filed as required by such laws; (ii) the Indenture has been duly authorized by the Company and the Trustee by all necessary corporate action; (iii) the Indenture has been duly executed and delivered by the Company and the Trustee and has been qualified under the Trust Indenture Act of 1939, as amended; (iv) the terms of the Debt Securities and their issuance and sale, including as to any Ordinary Shares to be issued on the conversion thereof, have been duly authorized by the Company by all necessary corporate action and the Indenture has been qualified under the Trust Indenture Act of 1939, as amended; (v) the terms of the Debt Securities and of their issuance and sale have been duly established in conformity with the Indenture so as not to violate any applicable law or result in a default under or breach of any agreement or instrument binding upon the Company, so as to be in conformity with the Company’s then operative articles of association (the “Articles of Association”), and so as to comply with any requirement or restriction imposed by any court or governmental body having jurisdiction over the Company; and (vi) the notes representing the Debt Securities have been duly executed and delivered by the Company and authenticated by the Trustee pursuant to the Indenture and delivered against payment therefor, then the Debt Securities, when issued and sold in accordance with the Indenture and a duly authorized, executed and delivered purchase, underwriting or similar agreement will be binding obligations of the Company, except as may be limited by bankruptcy, insolvency, reorganization, moratorium or other similar laws relating to or affecting creditors’ rights generally, and by general equitable principles (regardless of whether considered in a proceeding at law or in equity).

2. With respect to the Warrants issued under a Warrant Agreement and offered under the Registration Statement, provided that (i) the Registration Statement and any required post-effective amendment thereto have become effective under the Securities Act and the Base Prospectus and any and all Prospectus Supplement(s) required by applicable laws have been delivered and filed as required by such laws; (ii) the Warrants and any Warrant Agreement have been duly authorized by the Company by all necessary corporate action; (iii) the applicable Warrant Agreement has been duly executed and delivered by the Company; (iv) the issuance and terms of the Warrants have been duly authorized by the Company

Abivax SA

June 30, 2026

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by all necessary corporate action; (v) the terms of the Warrants and of their issuance and sale have been duly established in conformity with the applicable Warrant Agreement and as described in the Registration Statement, the Base Prospectus and the related Prospectus Supplement(s), so as to be in compliance with and not violate any applicable law or result in a default under or breach of any agreement or instrument binding upon the Company, so as to be in conformity with the Articles of Association, and so as to comply with any requirement or restriction imposed by any court or governmental body having jurisdiction over the Company; and (vi) the Warrants have been duly executed and delivered by the Company pursuant to the applicable Warrant Agreement and delivered against payment therefor, then the Warrants, when issued and sold in accordance with the applicable Warrant Agreement and a duly authorized, executed and delivered purchase, underwriting or similar agreement will be binding obligations of the Company, except as may be limited by bankruptcy, insolvency, reorganization, moratorium or other similar laws relating to or affecting creditors’ rights generally, and by general equitable principles (regardless of whether considered in a proceeding at law or in equity).

Our opinion set forth above is limited to the matters expressly set forth in this letter, and no opinion has been or should be implied, or may be inferred, beyond the matters expressly stated. This opinion speaks only as to law and facts in effect or existing as of the date hereof, and we have no obligation or responsibility to update or supplement this opinion to reflect any facts or circumstances that may hereafter come to our attention or any changes in law that may hereafter occur.

We hereby consent to the filing of this opinion as an exhibit to the Registration Statement and to the reference to our firm under the caption “Legal Matters” in the Base Prospectus. In giving such consent, we do not thereby admit that we are in the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations of the Commission thereunder.

 

Sincerely,
Cooley LLP
By:		/s/ Divakar Gupta
		Divakar Gupta