Public healthSep 7, 2025

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

mRNA Technology Weekly Brief ↗PubMed ↗DOI ↗

Updated Jun 28, 2026

Abstract

Essence

In Danish adolescents, BNT162b2 protection against SARS-CoV-2 infection was limited and waned substantially over time.

Evidence

Register-based observational target-trial emulation matched 235,636 vaccinated adolescents aged 12-15 years to 235,636 unvaccinated peers and found estimated effectiveness against mild infection fell from 42.88% within 25 days to about 8.85%-8.37% at 320 days, while effectiveness against moderate infection fell from 53.71% to about 22.06%-22.73%.

Caveat

This was an observational real-world study rather than a randomized trial, and severe infection was too rare to estimate reliably, with only 5 events in vaccinated adolescents and 14 in unvaccinated adolescents.

Simplified

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.