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The results of 2 large studies comparing severe disease and death among individuals vaccinated against COVID-19 support a benefit of booster doses. Both studies were conducted in Israel, where BNT162b2 (Pfizer-BioNTech) boosters were introduced in July 2021.
One analysis included data from more than 840 000 vaccinated people aged 50 years or older, 90% of whom received a booster dose. The death rate was 0.16 per 100 000 persons per day in the booster group compared with 2.98 per 100 000 persons per day in the nonbooster group. The other study involved almost 4.7 million vaccinated individuals aged 16 years or older. Across age groups, COVID-19 cases and severe illness were substantially lower among those who received a booster, as were deaths among those aged 60 years or older who were boosted.
Together, the findings indicated that COVID-19 boosters have a relative effectiveness of 90% to 95% against severe disease or death, according to an editorial that accompanied the studies in the New England Journal of Medicine. “This means that if the absolute effectiveness of two vaccine doses is 90%, the absolute effectiveness of two doses plus a booster is 99 to 100%,” the editorialist, Minal K. Patel, MD, of the US Centers for Disease Control and Prevention’s COVID-19 Response International Task Force, wrote.
The studies, Patel added, “provide much-needed evidence of the effectiveness of the booster dose.” She noted, however, that in 105 countries, less than 40% of the population has received a full primary vaccine series and that increasing primary vaccination uptake throughout the world will make the most difference in preventing severe COVID-19 illness and death.