BNT162b2 vaccine booster dose protection: A nationwide study from Israel

Abstract

Background: On July 30, 2021, a third (booster) dose of the Pfizer BNT162b2 vaccine was approved in Israel for individuals 60 years or older who had been fully vaccinated (i.e., received two doses) at least five months previously. Here, we estimate the reduction in relative risk for confirmed infection and severe COVID-19 provided by the booster dose. Methods: 1,144,690 individuals aged 60y and older who were eligible for a booster dose were followed between July 30 and August 22, 2021. We defined dynamic cohorts where individuals initially belong to the 'non-booster' cohort, leave it when receiving the booster dose and join the 'booster' cohort 12 days later. Rates of infection and severe COVID-19 outcomes per person-days at risk were compared between the cohorts using Poisson regression, adjusting for possible confounding factors. Results: Twelve days or more after the booster dose we found an 11.4-fold (95% CI: [10.0, 12.9]) decrease in the relative risk of confirmed infection, and a >10-fold decrease in the relative risk of severe illness. Under a conservative sensitivity analysis, we find ≈5-fold protection against confirmed infection. Conclusions: In conjunction with safety reports, this study demonstrates the effectiveness of a third vaccine dose in both reducing transmission and severe disease and indicates the great potential of curtailing the Delta variant resurgence by administering booster shots.

The Immune Response to SARS-CoV-2 and Variants of Concern

“…On the 30 July 2021, a third dose of BNT162b2 was approved in Israel for people over 60 years old who had been vaccinated at least 5 months previously. In an analysis of data to the 24 August 2021, increased short term protection against confirmed infection and severe disease was reported with the third dose [133]. Further follow-up is required to determine whether a third dose increases vaccine effectiveness long term.…”

The Mask-Wearing Bias In The Estimates Of Vaccine Efficacy

“…In other countries the degree to which the response to COVID19 is polarized appears to be less, and so we can expect the mask-vaccine correlation to be less pronounced. Moreover, the countries that enforce masking (especially for the unvaccinated), vaccine passports and other public health measures more effectively than the US can be expected to have zero or negative correlation between vaccination and avoidance of exposure 4 to the SARS-Cov2 virus. For example, in a country that has a functional vaccination passport system the vaccinated would be able to attend large gatherings more than the unvaccinated.…”

“…We can now evaluate the adjustment factor necessary to compute the true risk from the observed risk. Using (4,5,6) and ( 8),…”

“…Thought this paper, when we speak of mask wearing, we include all other infection-avoidance techniques, such as physical distancing, avoidance of crowded conditions or indoor spaces, isolation and the like 4. Thus, a positive correlation between the vaccination and exposure level.…”

“…It is ironic that by rejecting masks the anti-vaccine crowd has succeeded in biasing the estimates of vaccine effectiveness upward and thus leading some in the CDC to believe that the third doses are unnecessary for the general population 10. A very recent study from Israel[4] has a detailed analysis of behavior around the time of (third) vaccination, addressing the biases described in[5]. Because that study compares the persons who already had two doses to those who got three, it is unlikely to be affected by ardent vaccine and mask rejectors.…”