Enanta patent ruled invalid in Pfizer Paxlovid case

The UPC’s decision addressed both patent validity and an infringement action concerning Paxlovid in 18 participating EU member states.

Rhea-AI Filing Summary

Enanta Pharmaceuticals, Inc. reported that the Unified Patent Court (UPC) concluded its European Patent No. EP 4 051 265 was invalid and that the company’s infringement action against Pfizer Inc. was unfounded. Enanta had brought the action over Pfizer’s manufacture, use and sale of Paxlovid in the 18 EU member states participating in the UPC; Pfizer counterclaimed to revoke the patent. The UPC held a hearing on September 29, 2026, and released its decision on October 29, 2026.

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• Major pointPatent ruling: The UPC concluded that Enanta’s ’265 Patent was invalid and that its infringement action was unfounded.

8-K Event Classification

Item 8.01 — Other Events

1 item

Item 8.01 Other Events Other

Voluntary disclosure of events the company deems important to shareholders but not covered by other items.

Key Figures

EU member states in UPC action: 18 EU member states Hearing date: September 29, 2026 Decision date: October 29, 2026

3 metrics

EU member states in UPC action 18 EU member states States participating in the UPC where the action concerned Pfizer’s manufacture, use and sale of Paxlovid

Hearing date September 29, 2026 UPC hearing on the infringement action and counterclaim for revocation

Decision date October 29, 2026 UPC released its decision on patent validity and the infringement action

Key Terms

Unified Patent Court, patent infringement action, counterclaimed for revocation

3 terms

Unified Patent Court regulatory

"in the Unified Patent Court (the “UPC”) of the European Union"

A unified patent court is a single legal forum that hears and decides patent disputes across multiple countries at once, acting like one central courtroom instead of many separate national courts. For investors, it matters because decisions there can affect the value and enforceability of a company’s patents across a whole region at once—similar to a single referee whose ruling changes the score for every team—impacting revenue risk, litigation costs and long-term competitive advantage.

patent infringement action regulatory

"filed a patent infringement action"

A patent infringement action is a legal lawsuit brought by a patent holder who alleges someone else has made, used, sold, or offered to sell an invention without permission. It matters to investors because the outcome can change a company’s ability to sell products, lead to damages or licensing fees, or force product changes—similar to a property dispute that can block or alter how someone uses a valuable asset.

counterclaimed for revocation regulatory

"Pfizer counterclaimed for revocation of the ’265 Patent"

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

What did the UPC decide in ENTA’s patent case against Pfizer?

The UPC concluded that Enanta’s European Patent No. EP 4 051 265 was invalid and that the company’s infringement action against Pfizer was unfounded. The decision followed a hearing on September 29, 2026; the action concerned Pfizer’s manufacture, use and sale of Paxlovid in the 18 EU member states participating in the UPC. Pfizer had counterclaimed for revocation.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Available on EDGAR 10/29/2026 - 04:05 PM EDT Accepted by SEC EDGAR 10/29/2026 - 04:05 PM EDT Learn about SEC filing dates

false000117764800011776482026-10-292026-10-29

UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
WASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): October 29, 2026

ENANTA PHARMACEUTICALS, INC.

(Exact name of Registrant as Specified in Its Charter)

Delaware			001-35839	04-3205099
(State or Other Jurisdiction of Incorporation)			(Commission File Number)	(IRS Employer Identification No.)
4 Kingsbury Avenue
Watertown, Massachusetts				02472
(Address of Principal Executive Offices)				(Zip Code)

Registrant’s Telephone Number, Including Area Code: (617) 607-0800

Not Applicable

(Former Name or Former Address, if Changed Since Last Report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

☐Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

☐Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

☐Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

☐Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act:

Title of each class		Trading Symbol(s)		Name of each exchange on which registered
Common Stock, par value $0.01 per share		ENTA		Nasdaq Global Select Market

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter).

Emerging growth company ☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Item 8.01 Other Events.

As previously disclosed, Enanta Pharmaceuticals, Inc. (the “Company”) filed a patent infringement action in the Unified Patent Court (the “UPC”) of the European Union against Pfizer Inc. and certain of its subsidiaries, seeking a determination of liability for infringement of European Patent No. EP 4 051 265 (the “‘265 Patent”) in connection with Pfizer’s manufacture, use, and sale of Paxlovid™ (nirmatrelvir tablets; ritonavir tablets) in the 18 EU member states participating in the UPC. Pfizer counterclaimed for revocation of the ’265 Patent. A hearing on the infringement action and counterclaim for revocation was held on September 29, 2026. On October 29, 2026, the UPC released its decision concluding that the ‘265 Patent is invalid. The UPC also determined that the infringement action was unfounded in light of its decision on validity.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

			ENANTA PHARMACEUTICALS, INC.
Date:	October 29, 2026	By:	/s/ Jay R. Luly, Ph.D.
			Jay R. Luly, Ph.D. President and Chief Executive Officer

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