-Enanta Pharmaceuticals, Inc. (NASDAQ: ENTA), a clinical-stage biotechnology company dedicated to creating novel, small molecule drugs for viral infections and immunological diseases, announced today that it has filed suit in the Unified Patent Court (UPC) of the European Union against Pfizer Inc. and certain of its subsidiaries (action number 35071/2025), seeking a determination of liability for use and infringement of European Patent No. EP 4 051 265 (the ’265 Patent) in the manufacture, use and sale of Pfizer’s COVID-19 antiviral, Paxlovid™ (nirmatrelvir tablets; ritonavir tablets). This enforcement action targets Pfizer’s activities in the 18 countries of the European Union that are presently participating in the UPC.

The European Patent Office’s recent grant of the ‘265 Patent to Enanta was published in the European Patent Bulletin today. The ‘265 Patent is based on Enanta’s July 2020 patent application describing coronavirus protease inhibitors invented by Enanta scientists. The ‘265 Patent is the European counterpart of U.S. Patent No. 11,358,953 (the ’953 Patent) involved in ongoing U.S. litigation between Enanta and Pfizer Inc.

Under UPC procedures, a hearing on the infringement action is expected to occur within the UPC’s published 12-month target, with the decision rendered within weeks thereafter. If the UPC determines there has been infringement, subsequent proceedings would be required to determine damages. All timelines remain subject to potential rights of appeal and other customary proceedings in European patent litigation.