The BNT162b2 COVID-19 vaccine manufactured by Pfizer and BioNTech demonstrated 95% efficacy in preventing symptomatic SARS-CoV-2 infection in a phase 3, placebo-controlled randomized clinical trial,1 and became the first COVID-19 vaccine to receive Emergency Use Authorization by the US Food and Drug Administration.2 On December 19, 2020, 8 days after the US Food and Drug Administration authorization, a large-scale campaign was launched in Israel to vaccinate its population.3 Health care workers were among the first eligible for vaccination, along with individuals at risk of COVID-19 complications and death. Concurrently with the vaccination campaign, the number of new COVID-19 cases surged in Israel, with up to 10 000 new cases per day (eFigure 1 in the Supplement),4,5 possibly due to the spread of the B.1.1.7 SARS-CoV-2 variant.
Analysis of uncontrolled data from the Israeli vaccination campaign has been consistent with the results from the phase 3 randomized clinical trial. The risk ratio for symptomatic disease, estimated from a cohort of more than 500 000 vaccinated adults and matched unvaccinated controls, was 0.06.8 However, the association of BNT162b2 vaccination with asymptomatic infection and transmission remains unclear, with important implications for public health policy. Data on vaccine effectiveness for health care workers, who are frequently at risk of exposure to SARS-CoV-2, are also limited. Asymptomatically infected individuals are estimated to account for 40% to 45% of all SARS-CoV-2 infections and may silently spread the virus for extended periods. Asymptomatic infections have been proposed as a major barrier to controlling the spread of SARS-CoV-2 infection and are a possible explanation for the rapid evolution of the COVID-19 pandemic.
This study was conducted to assess the association between vaccination with the BNT162b2 vaccine and SARS-CoV-2 infections among health care workers at a tertiary medical center in Tel Aviv, Israel. Periodic screening for SARS-CoV-2 infection, coupled with detailed investigation of each infection confirmed via polymerase chain reaction (PCR) tests, allowed reliable estimation of symptomatic and asymptomatic infection rates.
