FRIDAY, April 8, 2022 (HealthDay News) — The rates of confirmed severe acute respiratory syndrome coronavirus 2 infection and severe COVID-19 were lower after receipt of a fourth dose of BNT162b2 vaccine, according to a study published online April 5 in the New England Journal of Medicine.

Yinon M. Bar-On, from the Weizmann Institute of Science in Rehovot, Israel, and colleagues extracted data on 1,252,331 persons aged 60 years and older and eligible for the fourth dose during a period of omicron predominance. The rate of confirmed infection and severe COVID-19 was estimated as a function of time starting at eight days after receipt of the fourth dose compared to those who had received only three doses and those who had received a fourth dose three to seven days earlier (four-dose group, three-dose group, and internal control group, respectively).

The researchers found that the number of cases of severe COVID-19 per 100,000 person-days was 1.5, 3.9, and 4.2 in the aggregated four-dose group, the three-dose group, and the internal control group, respectively. The adjusted rate of severe COVID-19 in the fourth week after receipt of the fourth dose was 3.5-fold and 2.3-fold lower than in the three-dose group and the internal control group, respectively. During the six weeks after receipt of the fourth dose, protection against severe illness did not wane. The adjusted rate of confirmed infection in the fourth week was 2.0-fold and 1.8-fold lower after receipt of the fourth dose than in the three-dose and internal control groups, respectively; this protection waned in later weeks.

“A fourth dose appeared to increase the protection against severe illness relative to three doses that were administered more than four months earlier,” the authors write.

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