BNT162b2 Vaccine Effectiveness in Preventing Asymptomatic Infection With SARS-CoV-2 Virus: A Nationwide Historical Cohort Study

Galia Zacay, David Shasha, Ronen Bareket, Itai Kadim, Fabienne Hershkowitz Sikron, Judith Tsamir, David Mossinson, Anthony D. Heymann*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Background: There is strong evidence regarding the efficacy and effectiveness of the BNT162b2 vaccine in preventing symptomatic infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). There is a relative paucity of data regarding its effectiveness in the prevention of asymptomatic infection. Methods: In this real-world observational study, we identified a subpopulation of individuals in a large health maintenance organization who were repeatedly tested for SARS-CoV-2 infection by polymerase chain reaction (PCR). We included these individuals in the study cohort and compared those who were vaccinated with BNT162b2 mRNA vaccine to unvaccinated individuals. A positive SARS-CoV-2 PCR test result was used as the outcome. The follow-up period was from January 1, 2021, until February 11, 2021. Results: A total of 6286 individuals were included in the cohort. Seven days after the second vaccine dose, a rate of 6 positive PCR tests per 10 000 person-days was recorded, compared with a rate of 53 positive tests per 10 000 person-days for the unvaccinated group. The estimated vaccine effectiveness against infection with SARS-CoV-2 virus after 2 vaccine doses was 89% (95% CI, 82%-94%). The estimated effectiveness 2 weeks after the first vaccine dose was 61% (95% CI, 49%-71%). Conclusions: In this study, vaccination with BNT162b2 reduced infection rates among individuals who underwent screening by frequent SARS-CoV-2 PCR testing. Using a cohort of frequently tested individuals reduced the indication bias for the PCR testing, which enabled estimation of infection rates.

Original languageEnglish
Article numberofab262
JournalOpen Forum Infectious Diseases
Issue number6
StatePublished - 1 Jun 2021


  • asymptomatic infection
  • COVID-19
  • observational study
  • SARS-CoV-2
  • vaccine effectiveness


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