Risk for Severe COVID-19 and Death Plummets With Pfizer Booster

Marcia Frellick

December 08, 2021

The Pfizer/BioNTech booster lowers the risk for confirmed illness, severe illness, and death from COVID-19, according to two large studies from Israel published today in the New England Journal of Medicine.

Both studies were completed before the advent of the Omicron variant.

In one study that included data on more than 4 million patients, led by Yinon M. Bar-On, MSc, of the Weizmann Institute of Science in Rehovot, Israel, the rate of confirmed SARS-CoV-2 infection was lower in the booster group than in the non-booster group by a factor of about 10.

This was true across all five age groups studied (range among the groups [starting with age 16], 9.0 to 17.2).

The risk for severe COVID-19 in the primary analysis decreased in the booster group by a factor of 17.9 (95% CI, 15.1 - 21.2), among those 60 years of age or older. Risk for severe illness in those ages 40-59 was lower by a factor of 21.7 (95% CI, 10.6 - 44.2).

Among the 60 and older age group, risk for death was also reduced by a factor of 14.7 (95% CI, 10.0 - 21.4).

Researchers analyzed data for the period from July 30 to October 10, 2021, from the Israel Ministry of Health database on 4.69 million people at least 16 years old who had received two Pfizer doses at least 5 months earlier.

In the main analysis, the researchers compared the rates of confirmed COVID-19, severe disease, and death among those who had gotten a booster at least 12 days earlier with the rates in a non-booster group.

The authors write: "Booster vaccination programs may provide a way to control transmission without costly social-distancing measures and quarantines. Our findings provide evidence for the short-term effectiveness of the booster dose against the currently dominant [D]elta variant in persons 16 years of age or older."

Death Risk Down by 90%

A second study in the NEJM , led by Ronen Arbel, PhD, with the Community Medical Services Division, Clalit Health Services, in Tel Aviv, Israel, which included more than 800,000 participants, also found mortality risk was greatly reduced among those who received the booster compared with those who didn't get the booster.

Participants age 50 or older who received a booster at least 5 months after a second Pfizer dose had 90% lower mortality risk due to COVID-19 than participants who did not get the booster.

The adjusted hazard ratio for death as a result of COVID-19 in the booster group, as compared with the non-booster group, was 0.10; 95% CI, 0.07 - 0.14; P < .001. Of the 843,208 eligible participants 758,118 (90%) received the booster during the 54-day study period.

The study included all Clalit Health Services (CHS) members who were age 50 or older on the study start date and had received two Pfizer doses at least 5 months earlier. CHS covers about 52% of the Israeli population and is the largest of four healthcare organizations in Israel that provide mandatory healthcare.

The authors note that although the study period was only 54 days (August 6-September 29), during that time "the incidence of COVID-19 in Israel was one of the highest in the world."

Authors of both original articles point out that the studies are limited by short time periods and that longer-term studies are needed to see how the booster shots stand up to known and future variants, such as Omicron.

Disclosures for authors of the Bar-On et al study are available with the full text. Authors of the Ronen et al study have disclosed no relevant financial relationships.

New Engl J Med. Published online December 8, 2021. Bar-On et al study, Arbel et al study

Marcia Frellick is a freelance journalist based in Chicago. She has previously written for the Chicago Tribune, Science News, and Nurse.com, and was an editor at the Chicago Sun-Times, the Cincinnati Enquirer, and the St. Cloud (Minnesota) Times. Follow her on Twitter at @mfrellick

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