Enanta Sues Pfizer Over COVID-19 Treatment Patent Infringement in Europe

Enanta Pharmaceuticals has sued Pfizer in Europe's Unified Patent Court for allegedly infringing a European patent related to Pfizer's Covid-19 treatment, Paxlovid. Enanta claims Pfizer's patent is based on their own research and that infringement proceedings will take place within 12 months. If found guilty, further proceedings would be necessary to assess damages. Pfizer's shares closed slightly up, while Enanta's shares rose by 5.1%.

Enanta Pharmaceuticals, Inc. (NASDAQ: ENTA) has filed a patent infringement lawsuit against Pfizer Inc. in the European Union's Unified Patent Court (UPC), alleging that Pfizer's COVID-19 antiviral, Paxlovid, infringes on Enanta's European Patent No. EP 4 051 265. The lawsuit, action number 35071/2025, targets Pfizer's activities in 18 EU countries and is based on Enanta's patent application for coronavirus protease inhibitors. A hearing is expected within 12 months, with a decision to follow, and potential subsequent proceedings to determine damages [1].

The patent at the center of the dispute, EP 4 051 265, was granted by the European Patent Office and is the European counterpart to U.S. Patent No. 11,358,953, which is involved in ongoing U.S. litigation between Enanta and Pfizer Inc. [2]. Enanta's patent is based on a July 2020 application describing coronavirus protease inhibitors invented by the company's scientists.

Under UPC procedures, a hearing on the infringement action is expected to occur within the court's 12-month target timeframe, with the decision anticipated within weeks thereafter. If the UPC determines infringement occurred, subsequent proceedings would be required to determine damages. All timelines remain subject to potential appeals and other customary proceedings in European patent litigation [3].

Enanta Pharmaceuticals is dedicated to creating novel, small molecule drugs for viral infections and immunological diseases. The company's clinical programs are currently focused on respiratory syncytial virus (RSV) and its earlier-stage immunology pipeline aims to develop treatments for inflammatory diseases by targeting key drivers of the type 2 immune response, including KIT and STAT6 inhibition. Glecaprevir, a protease inhibitor discovered by Enanta, is part of one of the leading treatment regimens for curing hepatitis C virus (HCV) infection and is sold by AbbVie in numerous countries under the tradenames MAVYRET® (U.S.) and MAVIRET® (ex-U.S.) [1].

Enanta's filing of this suit is part of its ongoing efforts to protect its intellectual property in the area of small-molecule drug development. The company cautions investors not to place undue reliance on forward-looking statements, as actual outcomes and results may differ materially from what is expressed in such statements [3].

References:
[1] https://www.ainvest.com/news/enanta-files-patent-infringement-suit-pfizer-covid-19-antiviral-patent-2508/
[2] https://www.investing.com/news/company-news/enanta-files-patent-infringement-suit-against-pfizer-over-paxlovid-93CH-4201876
[3] https://www.morningstar.com/news/business-wire/20250820282912/enanta-pharmaceuticals-files-patent-infringement-suit-against-pfizer-in-the-unified-patent-court-of-the-european-union