Federal Circuit Voids Patent Over One-Character Provisional Error
A Federal Circuit panel invalidated a Covid-19 treatment patent, finding a one-character difference between a provisional application and the issued patent fatal to its priority claim against Pfizer's intervening prior art.
The U.S. Court of Appeals for the Federal Circuit affirmed the invalidation of an Enanta Pharmaceuticals patent for a coronavirus treatment, holding it could not claim priority to its 2020 provisional application because of a critical one-character discrepancy. The provisional disclosed a chemical group starting with two carbon atoms ("C2-C12"), while the later patent claimed a group that also included the one-carbon option ("C1-C12"). The court rejected arguments that this was a correctable typo, stating "C2 is simply different from C1."
This seemingly minor drafting error was enough to break the priority chain. As a result, Pfizer’s subsequent disclosure of nirmatrelvir, the active ingredient in its blockbuster drug Paxlovid, became invalidating prior art that anticipated Enanta's claims. The ruling underscores the exacting standards for written description support and highlights the immense financial consequences of even small errors in patent prosecution. The case serves as a stark warning for patent counsel to meticulously proofread provisional applications and to ensure they describe specific, meaningful combinations, not just a broad universe of possible components.