Clinical Question

To what extent does a third dose of the Pfizer-BioNTech vaccine protect against symptomatic illness and hospitalization from COVID-19 in patients 60 years and older?

Bottom Line

A third booster dose of the Pfizer-BioNTech mRNA vaccine against COVID-19 provides a large increase in protection for people 60 years and older against mild and severe infection. The protection against mild infection could help reduce community spread and reduce the incidence of long COVID in some infected patients. (Level of Evidence = 2c)

Synopsis

Israel had vaccinated one-half of its population by the end of March 2021 and began to roll out vaccine boosters in July because of concerns over waning immunity. One study looked at the period from July 30 to August 30, 2021, using data from a government health registry with information about vaccination status, age, demographics, hospitalizations, and COVID-19 infections. The authors identified 1,137,804 people 60 years and older who had not been previously infected with COVID-19 and who were in the country (Israel) in August. They compared the rates of any severity of COVID-19 infection in those who had received the booster with those who had not. They used a Poisson regression to adjust for age, sex, demographics, and the date of the patient's second vaccine dose. They found that the risk of any infection was much higher (adjusted risk ratio = 11.3; 95% CI, 10.4 to 12.3), as was the risk of severe infection (adjusted risk ratio = 19.5; 95% CI, 12.9 to 29.5), in the group who did not receive a vaccine booster. There was no added protection in the first week after the booster; the protection rose to substantial levels approximately 12 to 16 days after the booster was received. A limitation of the study was that care-seeking behavior may have differed between groups. This is accounted for in the test-negative control strategy used for most studies of vaccine efficacy, but that was not possible with this dataset. The duration of follow-up was less than a month, so durability remains unknown.

Study design: Cohort (retrospective)

Funding source: Unknown/not stated

Setting: Population-based

Reference: Bar-On YM, Goldberg Y, Mandel M, et al. Protection of BNT162b2 vaccine booster against Covid-19 in Israel. N Engl J Med. 2021;385(15):1393–1400.

Editor's Note: Dr. Ebell is deputy editor for evidence-based medicine for AFP and cofounder and editor-in-chief of Essential Evidence Plus, published by Wiley-Blackwell.