Fourth dose of Pfizer-BioNTech COVID-19 vaccine is effective in persons 60 and older

Reference

Magen O, Waxman JG, Makov-Assif M, et al. Fourth dose of BNT162b2 mRNA Covid-19 vaccine in a nationwide setting. N Engl J Med 2022;386(17):1603-1614.

Synopsis

This study in a large Israeli health system identified 182,122 persons 60 years or older who had received a fourth dose of the Pfizer-BioNTech mRNA vaccine against COVID-19 (BNT162b2). The persons had all received their third dose at least 4 months previously, and none had a previous confirmed COVID-19 infection. Each person was matched with a person who had not yet received their fourth dose (the matching was based on demographics, area of residency, number of chronic conditions, and the number of hospitalizations in the previous 3 years). Each pair was followed up for up to 30 days; if the control person received a fourth dose during that period, both members of the pair were dropped. The groups were very similar at baseline, with a median age of 72 years, 53% were women, and they had similar numbers of comorbidities and hospitalizations. Vaccine efficacy between 7 days and 30 days was 45% against infection, 55% against symptomatic infection, 68% against hospitalization, 62% against severe COVID-19, and 74% against death. Among those with a COVID-19 infection during days 7 to 30, the likelihood of hospitalization was 2.0% in the 4-dose group and 3.4% in the 3-dose group. Similarly, the likelihood of death among those infected with COVID-19 was 0.17% in the 4-dose group and 0.39% in the 3-dose group. I calculated the numbers needed to immunize as 34 to prevent one infection between days 7 and 30, 673 to prevent one hospitalization, and 5228 to prevent one death. Those numbers will be smaller (ie, more favorable) over a longer time horizon. A second study in the same journal confirmed these benefits, and also found that although protection against infection waned relatively quickly, protection against severe disease did not.