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

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.