Case Explained: ENANTA PHARMACEUTICALS, INC v. PFIZER INC

Court: United States Court of Appeals for the Federal Circuit Filed: 2026-06-23 The Federal Circuit affirmed the district court’s grant of summary judgment holding that all claims of Enanta’s U.S. Patent 11,358,953 are invalid as anticipated by Pfizer’s prior public disclosure of nirmatrelvir. The court determined that the patent was not entitled to claim priority from Enanta’s earlier provisional application because the provisional failed to provide adequate written description support for the claimed invention under 35 U.S.C. § 112. The court applied the standard that an applicant is entitled to the filing date of an earlier application only if the earlier application describes the later claimed invention with sufficient detail such that a person skilled in the art can conclude the inventor was “in possession” of the claimed invention as of the earlier filing date. The court rejected Enanta’s argument that a discrepancy between a written number (“one to twelve”) and a numeral (“C2-C12”) in a general definition section constituted an obvious typographical error justifying correction. The court reasoned that the specific disclosure of “—NHC(O)—C2-C12-alkyl” in the provisional application explicitly excluded one-carbon alkyl groups, and no genuine dispute of material fact existed regarding whether a skilled artisan would recognize the specific claim scope as disclosed. Consequently, because the patent could not claim priority from the provisional application’s filing date, the prior public disclosure by Pfizer anticipated the claims. As a result of this decision, Enanta’s patent claims remain invalid, and Pfizer is free to continue selling its product without liability for infringement based on these claims. Do It For The Case Law is a news reporting service. Nothing in this episode constitutes legal advice.