BNT162b2 mRNA Vaccine Effectiveness Given Confirmed Exposure: Analysis of Household Members of COVID-19 Patients

Abstract

Background

While BNT162b2 vaccine-efficacy analyses were previously published, the effectiveness of the vaccine in preventing COVID-19 given confirmed exposure has not been previously demonstrated, even though it has policy implications, such as the need for self-quarantine when exposure has occurred or protective measures for vaccinated individuals in high-risk areas.

Methods

In a retrospective cohort study, we used data collected between 20/12/2020 and 17/03/2021 from the second largest healthcare provider in Israel to analyze the probability of an additional household infection occurring within 10 days after an index infection. In model 1, vaccine effectiveness was described for Fully Vaccinated individuals (7 or more days from second dose) versus either Unvaccinated participants or those Recently Vaccinated Once (0-7 days from the first dose, presumably still unprotected). Secondary analyses included correction for differing testing rates. In model 2, we conducted a separate analysis of households comprised of only adults with the same vaccination status.

Results

173,569 households were included, of which 6,351 households had an index infection (mean [SD] age, 58.9 [13.5] years; 50% were women).Adjusted vaccine effectiveness of Fully Vaccinated compared to Unvaccinated participants was 80.3% [95% CI, 73.5 to 85.4] and 82.0% [95% CI, 75.6 to 86.8] compared to those Recently Vaccinated Once.

Conclusions

The BNT162b2 vaccine is effective in a high-risk real-life exposure scenario, but the protection rates afforded in these settings are lower than those previously described. Household members of patients infected with SARS-CoV-2 and individuals with a confirmed significant exposure to SARS-CoV-2 are still at risk of being infected even if fully vaccinated.