Study: Pfizer COVID vaccine efficacy wanes 27 days after dose 2 in teens

A new study finds waning Pfizer/BioNTech COVID-19 vaccine protection against symptomatic infection in Brazilian and Scottish teens starting 27 days after the second dose amid the Delta and Omicron variant waves, but protection against severe illness was still strong at 98 days in Brazil.

The study, published yesterday in The Lancet Infectious Diseases, analyzed nationwide data from 503,776 COVID-19 tests of 2,948,538 adolescents aged 12 to 17 years from Sep 2, 2021, to Apr 19, 2022, in Brazil, and 127,168 tests of 404,673 adolescents from Aug 6, 2021, to Apr 19, 2022, in Scotland. Protection against severe illness, defined as hospitalization or death within 28 days, was estimated only in Brazil owing to the small number of such cases in Scotland.

The researchers estimated vaccine effectiveness (VE) against symptomatic COVID-19 by comparing the time elapsed since the first or second dose in adolescents who tested positive on polymerase chain reaction (PCR) tests in Scotland, or by PCR or antigen test in Brazil, and those who tested negative (controls).

The period was marked by the Omicron surge in both countries, supplanting Delta in December 2021 in Scotland and January 2022 in Brazil. Vaccine rollout for this age-group began in August 2021 in Scotland and September 2021 in Brazil.