Effectiveness of mRNA COVID-19 Vaccines in Adolescents Over 6 Months

BACKGROUND AND OBJECTIVES: On June 4, 2021, Italy launched the coronavirus disease 2019 (COVID-19) vaccination of adolescents to slow down the COVID-19 spread. Although clinical trials have evaluated messenger ribonucleic acid (mRNA) vaccine effectiveness in adolescents, there is limited literature on its real-world effectiveness. Accordingly, this study aimed to estimate the effectiveness of mRNA COVID-19 vaccines against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and mild or severe COVID-19 in a cohort of Sicilian adolescents within a 6 month observation period.METHODS: A retrospective cohort study was conducted with adolescents aged 12 to 18 years, residents of Sicily, who were followed from July 15 to December 31, 2021. SARS-CoV-2 infections, mild and severe COVID-19, and COVID-19-related intubation or deaths during the study period were compared between subjects vaccinated with 2 doses of mRNA vaccines and unvaccinated individuals. The Cox regression analysis, adjusted for age and sex, was performed to compare the 2 groups.RESULTS: Overall, the study included a total at-risk population of 274 782 adolescents with 61.4% of them having completed the vaccination cycle by the end of the study. Unvaccinated subjects had higher incidence rates of SARS-CoV-2 (1043 x 10 000 vs 158.7 x 10 000 subjects), mild COVID-19 (27.7 x 10 000 vs 1.8 x 10 000 subjects) and severe COVID-19 (1.41 x 10 000 vs 0 subjects) compared with the vaccinated population. The estimated adjusted vaccine effectiveness against SARS-CoV-2 infection was 71.2%, reaching 92.1% and 97.9% against mild and severe COVID-19, respectively.CONCLUSIONS: This study provides rigorous evidence of mRNA COVID-19 vaccines' effectiveness in protecting adolescents from both SARS-CoV-2 infection and COVID-19.