Mortality Due to COVID-19 is Reduced by Receiving a Vaccine Booster

December 9, 2021
Giuliana Grossi

Among vaccinated individuals, results show a 90% lower mortality rate due to COVID-19 in the group that received a booster compared with those who did not.

The results of a new study found a 90% lower mortality due to COVID-19 in individuals that received a booster dose at least 5 months after a second dose of the BNT1662b2  vaccine (Pfizer-BioNTech) compared with individuals who did not receive a booster dose.

Ronen Arbel, PhD, Community Medical Services Division, Clalit Health Services, led a team of investigators to determine the effectiveness of the booster in lowering the mortality rate due to COVID-19.

The resurgence of COVID-19 cases in populations that had been vaccinated early after the emergence of the B.1.617.2 (delta) variant led to the approval of the third dose. Therefore, data were limited on its efficacy.

Understanding the Data

During the 54-day study period, 90% (758,118) of the total eligible individuals (843,208) received the booster. In the booster group, 65 participants died from COVID-19. In the control group, there were 137 deaths due to COVID-19.

In the booster group compared with the control group, the adjusted hazard ratio for death due to COVID-19 was 0.10 (95% confidence interval, 0.07 to 0.14; P<0.001).

The majority of the individuals (60%) were 65 years or older with a mean age of 68.5. Prominent coexisting conditions were hypertension (46%), obesity (33%), and diabetes (29%).

In the Cox regression model, confounding variables that were significantly associated with death due to COVID-19 included age, male sex, chronic kidney failure, lung cancer, and history of cerebrovascular accident.

Socioeconomic status, diabetes, chronic obstructive pulmonary disease, ischemic heart disease, chronic heart failure, obesity, history of transient ischemic attack, and history of smoking were not significantly associated with death due to COVID-19.

The hazard ratio for death in individuals up to 14 days after the administration of the booster, as compared with the control group, was 0.67 (95% CI, 0.60-0.74; P<0.001). The hazard ratio comparing the 2 groups for death within 7 days of the booster was 0.95 (95% CI, 0.86-1.05; P=0.32).

“Therefore,” investigators wrote, “our assumption of a 7-day lag time between the administration of the booster and booster effectiveness was confirmed.”

The Participants

On August 6, 2021, the study period began. This was 7 days after the approval of the booster in Israel for individuals 60 years of age or older. The study period concluded in September 2021.

Data were obtained from members of Clalit Health Services who were 50 years of age or older at the beginning of the study and had received 2 doses of the Pfizer-BioNTech vaccine at least 5 months earlier.

Mortality due to COVID-19 was examined among individuals who received the booster within the study period and was compared with the group of individuals who did not receive the booster.

In order to estimate the association of the booster status with death, while adjusting for sociodemographic factors and coexisting conditions, a Cox proportional-hazards regression model with time-dependent covariates was used.

Individuals were excluded from participation if they were missing data regarding date of birth or sex. Those who had already been infected with SARS-COV-2 or received a booster prior to the start of the study were also excluded.

“Our study showed that among participants who were 50 years of age or older and had received a second dose of the BNT162b2 vaccine at least 5 months earlier, those who received a booster had 90% lower mortality due to COVID-19 than those who did not receive a booster,” investigators wrote.

The study, “BNT162b2 Vaccine Booster and Mortality Due to COVID-19”, was published in The New England Journal of Medicine.


x