Enanta Pharmaceuticals, Inc. v. Pfizer Inc. (Fed. Cir., June 23, 2026) 2025-1427

In this episode, the United States Court of Appeals for the Federal Circuit affirmed a lower court's ruling that Enanta Pharmaceuticals' patent regarding coronavirus treatments is invalid. The central dispute involved whether a typographical error in a provisional application—listing a chemical range starting with two carbon atoms instead of one—could be corrected to secure an earlier priority date. Because the original filing failed to explicitly describe the specific one-carbon compound used in Pfizer’s Paxlovid, the court determined that Enanta did not technically possess the invention at the time of the initial filing. Consequently, Pfizer's public disclosure of its own antiviral medication preceded the patent's valid date, acting as anticipatory prior art that nullifies Enanta's claims. The court emphasized that written description requirements must be strictly met, noting that a disclosure of one chemical structure does not inherently support a different, albeit similar, structure.

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