Following a rise in cases due to the delta variant and evidence of waning immunity after 2 doses of the BNT162b2 vaccine, Israel began administering a third 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. In this study, we used data from Israel to estimate the protection of the 3rd dose against severe disease up to 7 months from receiving the booster dose. The analysis shows that protection conferred by the 3rd dose against omicron did not wane over a 7-month period and that a 4th dose further increased protection, with a severe disease rate approximately 3-fold lower than in the 3-dose cohorts.
Protection against omicron severe disease 0-7 months after BNT162b2 booster