tetano
Editor, Senior Moderator
Open Forum Infect Dis
. 2021 Jun 9;8(6)
fab262.
doi: 10.1093/ofid/ofab262. eCollection 2021 Jun.
BNT162b2 Vaccine Effectiveness in Preventing Asymptomatic Infection With SARS-CoV-2 Virus: A Nationwide Historical Cohort Study
Galia Zacay[SUP] 1 2 [/SUP], David Shasha[SUP] 1 2 3 [/SUP], Ronen Bareket[SUP] 1 2 [/SUP], Itai Kadim[SUP] 1 [/SUP], Fabienne Hershkowitz Sikron[SUP] 1 [/SUP], Judith Tsamir[SUP] 1 [/SUP], David Mossinson[SUP] 1 [/SUP], Anthony D Heymann[SUP] 1 2 [/SUP]
Affiliations
Abstract
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.
Keywords: COVID-19; SARS-CoV-2; asymptomatic infection; observational study; vaccine effectiveness.
. 2021 Jun 9;8(6)
fab262.doi: 10.1093/ofid/ofab262. eCollection 2021 Jun.
BNT162b2 Vaccine Effectiveness in Preventing Asymptomatic Infection With SARS-CoV-2 Virus: A Nationwide Historical Cohort Study
Galia Zacay[SUP] 1 2 [/SUP], David Shasha[SUP] 1 2 3 [/SUP], Ronen Bareket[SUP] 1 2 [/SUP], Itai Kadim[SUP] 1 [/SUP], Fabienne Hershkowitz Sikron[SUP] 1 [/SUP], Judith Tsamir[SUP] 1 [/SUP], David Mossinson[SUP] 1 [/SUP], Anthony D Heymann[SUP] 1 2 [/SUP]
Affiliations
- PMID: 34189176
- PMCID: PMC8231369
- DOI: 10.1093/ofid/ofab262
Abstract
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.
Keywords: COVID-19; SARS-CoV-2; asymptomatic infection; observational study; vaccine effectiveness.