
In a recent precedential decision by the Federal Circuit, the Court delivered a cautionary reminder that errors or omissions in a provisional patent application can have significant consequences for a patent’s priority claim and ultimately its validity.
In Enanta Pharmaceuticals, Inc. v. Pfizer, Inc., No. 2025-1427 (Fed. Cir. June 23, 2026), the Federal Circuit affirmed summary judgment that Enanta’s ’953 patent (U.S. 11,358,953) was not entitled to the priority date of its ’048 provisional application (Application No. 63/054,048) because the ’048 provisional lacked adequate written description support for a chemical substituent claimed in the ’953 patent. As a result, Pfizer’s public disclosure of its protease inhibitor, nirmatrelvir (the active ingredient in Paxlovid®), anticipated the claims of the ’953 patent, rendering the patent invalid.








