We compared SARS CoV-2 infection by vaccination status from February 1, 2021 to August 13, 2021 in the Veterans Health Administration, covering 2.7% of the U.S. population. Vaccine protection declined by mid-August 2021, decreasing from 91.9% in March to 53.9%. Declines were greatest for the Janssen vaccine followed by PfizerBioNTech and Moderna. Patterns of breakthrough infection over time were consistent by age, despite rolling vaccine eligibility, implicating the Delta variant as the primary determinant of infection.
