The effectiveness of two doses of the Pfizer/BioNTech COVID-19 vaccine against hospitalization for infections with the highly transmissible Omicron variant was 40% among adolescents 12 to 18 years and 68% among children aged 5 to 11, finds a test-negative study published yesterday in the New England Journal of Medicine (NEJM).

Led by the Centers for Disease Control and Prevention's (CDC's) COVID-19 Response Team, the study involved 1,185 COVID-19 patients admitted to 31 US pediatric hospitals and 1,627 controls aged 5 to 18 years admitted for other indications. The 918 adolescents were enrolled from Jul 1 to Dec 18, 2021 (Delta variant era) and from Dec 19, 2021, to Feb 17, 2022 (Omicron era).

The 267 children aged 5 to 11 were enrolled only during the Omicron period because the Pfizer vaccine wasn't authorized for that age-group until October 2021. Owing to insufficient numbers of severely ill patients in this age-group, VE against critical illness—defined as those who required life support, such as mechanical ventilation—couldn't be evaluated.

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