Breakthrough COVID-19 infection rate
Breakthrough infection among fully vaccinated individuals was defined
according to the US Centers for Disease Control and Prevention, as
infection occurring ≥14 days after the second dose in a two-dose series
or ≥14 days after a single-dose vaccine. Participants were queried for
evidence of breakthrough COVID-19 infection following each vaccine dose
and electronic medical records were reviewed for the evidence of
infection 6 months after each vaccination, based on the results of
positive SARS-CoV-2 PCR tests. Follow-up was 1 year after the first
vaccine dose.