European Patent Court Invalidates Paxlovid Patent, Finds Enanta’s Claim Against Pfizer Unfounded
Key Facts
Enanta Pharmaceuticals said the Unified Patent Court ruled on October 29, 2026, to invalidate European patent EP 4 051 265, which the company had relied on in a lawsuit against Pfizer over Paxlovid. In a filing with the U.S. Securities and Exchange Commission, Enanta said the court also found the infringement claim "unfounded" in light of its decision on the patent’s validity. The dispute concerned Enanta’s request to establish Pfizer’s liability for manufacturing, using and selling the drug. The ruling therefore combined a decision on Pfizer’s request to revoke the patent with the outcome of the infringement claim. The ruling closes this stage of the dispute before the court, according to the company’s filing.
The case concerns European patent EP 4 051 265, which Enanta said applies to the manufacture, use and sale of Paxlovid. The lawsuit extended to 18 European Union member states participating in the Unified Patent Court system, according to the filing. Pfizer filed a counterclaim seeking to revoke the patent, alongside its defense in the infringement case. The court held a hearing on the lawsuit and counterclaim on September 29, 2026. A month later, it ruled to invalidate the patent and then found the infringement claim unfounded on the basis of that ruling. This sets out the outcome Enanta announced in the case, without the filing describing any broader effect on the patent or other proceedings.
In January 2026, Enanta had outlined an expected timeline for the proceedings, saying the infringement hearing was expected within the court’s published target of 12 months and that a decision would follow within weeks of the hearing. The company added at the time that it expected to provide an update on the case in the second half of 2026. The hearing took place on September 29, followed by the ruling on October 29, according to the subsequent filing. These dates show the sequence from the timeline the company announced to the court hearing and ruling. Enanta’s expected update during the second half of the year included its announcement of the court’s decision and its outcome.
Enanta shares closed at $11.15 per share on October 29, 2026, the same date the company announced the court’s decision. Pfizer shares also closed at $29.95 that day, according to EL7 data. The closing prices provide a snapshot of the two stocks on the day of the announcement, but on their own they do not establish whether the ruling moved or affected trading. The price data did not include a comparison with the previous session’s close or a measure of the change during the day. The figures therefore describe closing levels on that date, while the announced ruling focused on invalidating the patent and finding the infringement claim unfounded.
In its financial results, Enanta reported revenue of $14.4 million for the three months ended June 30, 2026, compared with $18.3 million in the same period of 2025. The company attributed the decline mainly to lower AbbVie sales of hepatitis C treatments. Cash, cash equivalents and short- and long-term marketable securities totaled $211.5 million on June 30, 2026. Enanta said this balance was sufficient to fund its operations and existing programs through fiscal 2029. These figures show the company’s operating resources as reported in its financial results, alongside the legal development it announced in a separate filing.
Investors are watching the company’s announced operating milestones in the coming months. Enanta said it plans to report fourth-quarter fiscal results on November 16, 2026. In the fourth quarter of 2026, the company expected preliminary Phase 1 data for EDP-978. It also aims to begin the registered RESOLVE Phase 2b/3 trial of zelicapavir in adults at high risk from respiratory syncytial virus (RSV) during the same quarter. The company said preliminary Phase 2b data for zelicapavir are expected in 2027. These milestones are the next developments Enanta listed in its financial results, following the Unified Patent Court ruling announcement.