BNT162b2 Vaccine Effectiveness against Omicron in Children 5 to 11 Years of Age

Abstract

Background: Limited evidence is available on the real-world effectiveness of the BNT162b2 vaccine against coronavirus disease 2019 (Covid-19) and specifically against infection with the omicron variant among children 5 to 11 years of age.

Methods: Using data from the largest health care organization in Israel, we identified a cohort of children 5 to 11 years of age who were vaccinated on or after November 23, 2021, and matched them with unvaccinated controls to estimate the vaccine effectiveness of BNT162b2 among newly vaccinated children during the omicron wave. Vaccine effectiveness against documented severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and symptomatic Covid-19 was estimated after the first and second vaccine doses. The cumulative incidence of each outcome in the two study groups through January 7, 2022, was estimated with the use of the Kaplan-Meier estimator, and vaccine effectiveness was calculated as 1 minus the risk ratio. Vaccine effectiveness was also estimated in age subgroups.

Results: Among 136,127 eligible children who had been vaccinated during the study period, 94,728 were matched with unvaccinated controls. The estimated vaccine effectiveness against documented infection was 17% (95% confidence interval [CI], 7 to 25) at 14 to 27 days after the first dose and 51% (95% CI, 39 to 61) at 7 to 21 days after the second dose. The absolute risk difference between the study groups at days 7 to 21 after the second dose was 1905 events per 100,000 persons (95% CI, 1294 to 2440) for documented infection and 599 events per 100,000 persons (95% CI, 296 to 897) for symptomatic Covid-19. The estimated vaccine effectiveness against symptomatic Covid-19 was 18% (95% CI, -2 to 34) at 14 to 27 days after the first dose and 48% (95% CI, 29 to 63) at 7 to 21 days after the second dose. We observed a trend toward higher vaccine effectiveness in the youngest age group (5 or 6 years of age) than in the oldest age group (10 or 11 years of age).

Conclusions: Our findings suggest that as omicron was becoming the dominant variant, two doses of the BNT162b2 messenger RNA vaccine provided moderate protection against documented SARS-CoV-2 infection and symptomatic Covid-19 in children 5 to 11 years of age. (Funded by the European Union through the VERDI project and others.).

Figure 1. Enrollment and Matching.

Of 136,127 eligible children who had been vaccinated, 108,904 (80%) were successfully matched and included in at least one of the study groups: 94,728 were included in the vaccinated group, of whom 79,448 were originally included as members in the vaccinated group and 15,280 were initially matched as members of the unvaccinated group and then were rematched as members of the vaccinated group after receiving their first dose. A total of 29,456 children were originally included as members of the unvaccinated group but were vaccinated during the study follow-up period. Of these children, 15,280 were successfully rematched as members of the vaccinated group (for whom a new matched unvaccinated control was found); 14,176 were not. CHS denotes Clalit Health Services, PCR polymerase chain reaction, and SARS-CoV-2 severe acute respiratory syndrome coronavirus 2.

Figure 2. Cumulative Incidence of Documented SARS-CoV-2 Infection and Symptomatic Covid-19.

Panel A shows the cumulative incidence of documented SARS-CoV-2 infection, as confirmed by a positive PCR test. Panel B shows the cumulative incidence of symptomatic Covid-19. The dashed vertical line at day 28 represents 7 days after the second vaccine dose was scheduled to be administered and marks the time at which the main follow-up period starts (in the vaccine effectiveness analysis, the follow-up period for children who did not receive the second dose at the designated time was shifted according to the time they received the second dose). Shaded areas indicate the 95% confidence intervals, and plus signs censored data.