Protection against Omicron BA.1/BA.2 severe disease 0-7 months after BNT162b2 booster

Abstract

Following evidence of waning immunity against both infection and severe disease after 2 doses of the BNT162b2 vaccine, Israel began administering a 3rd BNT162b2 dose (booster) in July 2021. Recent studies showed that the 3rd dose provides a much lower protection against infection with the Omicron variant compared to the Delta variant and that this protection wanes quickly. However, there is little evidence regarding the protection of the 3rd dose against Omicron (BA.1/BA.2) severe disease. In this study, we estimate the preservation of immunity from severe disease up to 7 months after receiving the booster dose. We calculate rates of severe SARS-CoV-2 disease between groups of individuals aged 60 and above, comparing those who received two doses at least 4 months previously to those who received the 3rd dose (stratified by the time from vaccination), and to those who received a 4th dose. The analysis shows that protection conferred by the 3rd dose against Omicron severe disease did not wane over a 7-month period. Moreover, a 4th dose further improved protection, with a severe disease rate approximately 3-fold lower than in the 3-dose cohorts.

Fig. 1. Adjusted rates of severe illness.

Adjusted rates of severe illness per 100,000 risk days obtained from Poisson regression analysis for the study period January 16, 2022–March 12, 2022, adjusted for age category (60–69, 70–79, 80+), sex, sector, and exposure (based on epidemiological week). Error bars represent 95% confidence intervals, which are not adjusted for multiplicity.

Fig. 2. Study population.

The participants in the study included persons who were 60 years of age or older, who received 2nd dose at least 4 months before the end of the study, who were not infected by SARS-CoV-2 before the study period, had available data regarding sex and demographic sector, had not stayed abroad during the whole study period, and had not been vaccinated with a vaccine different from BNT162b2 before the study period.

Fig. 3. Vaccination dynamics.

Vaccination dynamics of people aged 60 or above during the study period. The dashed vertical lines represent the study period, between January 16, 2022, and March 12, 2022.