Since the start of the vaccination campaign, the development of COVID-19 has been reported in persons who have received one or both doses of mRNA-1273 (Moderna) or BNT162b2 (Pfizer) vaccine. Both the University of California, San Diego (UCSD) and the University of California, Los Angeles (UCLA) health systems began to vaccinate health care workers on December 16, 2020. On December 2, in addition to defining a low threshold for testing of symptomatic persons, UCSD mandated that asymptomatic health care workers undergo weekly testing by polymerase-chain-reaction (PCR) assay of nasal swabs. On December 26, UCLA instituted an optional testing program for asymptomatic health care workers with PCR assay of nasal swabs. This program has allowed for increased detection of asymptomatic SARS-CoV-2 infections after vaccination. From December 16, 2020, through February 9, 2021, a total of 36,659 health care workers received the first dose of vaccine, and 28,184 of these persons (77%) received the second dose. Among the vaccinated health care workers, 379 unique persons tested positive for SARS-CoV-2 at least 1 day after vaccination, and the majority (71%) of these persons tested positive within the first 2 weeks after the first dose. After receiving both vaccinations, 37 health care workers tested positive; of these workers, 22 had positive test results 1 to 7 days after the second dose. Only 8 health care workers tested positive 8 to 14 days after the second vaccination, and 7 tested positive 15 or more days after the second vaccination. As of February 9, a total of 5455 health care workers at UCSD and 9535 at UCLA had received the second dose 2 or more weeks previously; these findings correspond to a positivity rate of 0.05%. The authors concluded that the rarity of positive test results 14 days after administration of the second dose of vaccine is encouraging and suggests that the efficacy of these vaccines is maintained outside the trial setting.
Keehner J, Horton LE, Pfeffer MA, Longhurst CA, Schooley RT, Currier JS, Abeles SR, Torriani FJ. SARS-CoV-2 Infection after Vaccination in Health Care Workers in California. N Engl J Med. 2021 Mar 23:NEJMc2101927. doi: 10.1056/NEJMc2101927.