BNT162b2 Vaccine Booster and Mortality Due to COVID-19

Quick Takes

  • This is an observational study leveraging Israel’s Clalit Health Services Database, which covers approximately one half of the Israeli population.
  • The study compared the rates of COVID-19–related death and positive SARS-CoV-2 infection between recipients of the booster dose and nonrecipients.
  • Recipients of the booster dose aged ≥50 years had significantly lower COVID-19–related mortality and lower infection rates compared to nonrecipients.

Study Questions:

Is a booster dose of the BNT162b2 vaccine (Pfizer–BioNTech) effective at lowering mortality?

Methods:

The authors used the Clalit Health Services database in Israel, which covers approximately 52% of the Israeli population, to obtain data for participants over 50 years of age who received two doses of BNT162b2 ≥5 months earlier. They compared the mortality due to coronavirus disease 2019 (COVID-19) among participants who received the booster during the study period (booster group) to that of those who did not receive the booster (nonbooster group). The study period was defined as August 6, 2021—7 days after approval for the use of the booster in persons aged ≥60 years in Israel, and ended in September 2021. Cox proportional hazards modeling with time-varying covariates was used to assess the association between receiving a booster dose and death due to COVID-19 (primary outcome). The secondary outcome was confirmed severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections.

Results:

A total of 843,208 participants met the eligibility criteria, of whom 758,118 (90%) received the booster during the 54-day study period. The mean age of the cohort was 69 years, 60% of whom were aged ≥65 years. One half of participants were women. Death due to COVID-19 occurred in 65 participants in the booster group (0.16 per 100,000 persons per day) and in 137 participants in the nonbooster group (2.98 per 100,000 persons per day). The adjusted hazard ratio for death due to COVID-19 in the booster group, as compared with the nonbooster group, was 0.10 (95% confidence interval, 0.07-0.14; p < 0.001). Findings were consistent across age groups (>65 and ≤65 years) and between men and women. The booster dose was also associated with a lower incidence of positive SARS-CoV-2 infection (adjusted hazard ratio, 0.17; 95% confidence interval, 0.16-0.18; p < 0.001).

Conclusions:

Participants who received a booster ≥5 months after a second dose of BNT162b2 had 90% lower mortality due to COVID-19 compared to participants who did not receive a booster.

Perspective:

While observational, the study provides compelling evidence of the BNT162b2 booster dose’s effectiveness in reducing COVID-19–related mortality and infection rates. Findings are consistent with initial reports by the Israeli Ministry of Health. The booster was approved in Israel in July 2021, but was not mandatory, allowing for the conduct of this study given not all participants received the booster. The nonrandomized nature of the study certainly confers a selection bias, given the reasons for not having received the booster could not be accounted for. Nevertheless, the strength of the association, its known pathophysiologic underpinnings, and prior evidence of vaccine effectiveness increase confidence in the findings. Another limitation of the study is its short duration (54 days), limiting the ability to infer long-term booster effectiveness. Longer-term studies and studies of other vaccines are underway and will provide additional clarity.

Clinical Topics: COVID-19 Hub, Geriatric Cardiology, Prevention

Keywords: Coronavirus Infections, COVID-19, COVID-19 Vaccines, Geriatrics, Health Services, Immunization, Secondary, Israel, Primary Prevention, RNA, Viral, SARS-CoV-2, Vaccine Potency


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