Long-term comparative effectiveness of BNT162b2 vaccine on SARS-CoV-2 infection in adolescents: A register-based real-world study from Denmark

Sep 7, 2025Public health

Long-term protection of the BNT162b2 vaccine against COVID-19 infection in Danish adolescents

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mRNA Technology on OpenScience ↗PubMed ↗DOI ↗

Abstract

The estimated vaccine efficacy (VE) against mild infection in fully vaccinated adolescents declined from 42.88% up to 25 days after vaccination to 8.85%-8.37% by 320 days.

The study involved 235,636 vaccinated adolescents matched with 235,636 unvaccinated adolescents.
VE against moderate infection decreased from 53.71% up to 25 days to 22.06%-22.73% at 320 days.
Five cases of severe infection occurred among vaccinated individuals, compared to 14 cases among unvaccinated individuals.
The observed decline in VE may indicate waning effectiveness over time or potential viral mutations.

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OBJECTIVES: Contribute to data on the long-term real-world effectiveness of the BNT162b2 vaccine efficacy (VE) in adolescents.

STUDY DESIGN: This observational study from July 2021 to June 2022 was designed to emulate a target trial.

METHODS: Fully vaccinated adolescents 12-15 years of age were matched to unvaccinated adolescents. Outcomes were mild (positive PCR test without hospitalization), moderate (positive PCR test with hospitalization within 30 days), or severe infection (positive PCR test with intensive therapy or death within 30 days). VE was estimated as 1-risk ratio.

RESULTS: We compared 235,636 vaccinated adolescents with 235,636 matched unvaccinated adolescents. On mild infection, the estimated VE declined from 42.88 % up to 25 days after full vaccination, to 33.86 %-37.26 % at 100 days and 8.85 %-8.37 % at 320 days. Estimated VE on moderate infection declined from 53.71 % up to 25 days to 22.06 %-22.73 % up to 320 days. A total of 5 events of severe infection among vaccinated, and 14 among unvaccinated individuals was observed.

CONCLUSIONS: Our estimated VE is limited and rapidly decreasing over 11 months. These findings may be due to the vaccine's effect waning over time, or mutation of the virus.