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 × 10 000 vs 158.7 × 10 000 subjects), mild COVID-19 (27.7 × 10 000 vs 1.8 × 10 000 subjects) and severe COVID-19 (1.41 × 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.

中文翻译：

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mRNA COVID-19 疫苗在 6 个月以上的青少年中的有效性。

背景和目标 2021 年 6 月 4 日，意大利启动了针对青少年的 2019 年冠状病毒病 (COVID-19) 疫苗接种，以减缓 COVID-19 的传播。尽管临床试验评估了信使核糖核酸 (mRNA) 疫苗在青少年中的有效性，但关于其真实世界有效性的文献有限。因此，本研究旨在评估 mRNA COVID-19 疫苗在 6 个月观察期内对西西里青少年队列中严重急性呼吸系统综合症冠状病毒 2 (SARS-CoV-2) 感染和轻度或重度 COVID-19 的有效性。方法 对 2021 年 7 月 15 日至 12 月 31 日期间 12 至 18 岁的西西里岛居民青少年进行了一项回顾性队列研究。SARS-CoV-2 感染、轻度和重度 COVID-19、在研究期间比较了接种 2 剂 mRNA 疫苗的受试者和未接种疫苗的个体之间与 COVID-19 相关的插管或死亡情况。对年龄和性别进行了调整的 Cox 回归分析用于比较 2 组。结果 总体而言，该研究共包括 274 782 名青少年的高危人群，其中 61.4% 在研究结束时完成了疫苗接种周期。未接种疫苗的受试者的 SARS-CoV-2（1043 × 10 000 对 158.7 × 10 000 受试者）、轻度 COVID-19（27.7 × 10 000 对 1.8 × 10 000 受试者）和重度 COVID-19（1.41 × 10 000 对 0 个受试者）与接种疫苗的人群相比。估计调整后疫苗对 SARS-CoV-2 感染的有效性为 71.2%，对轻度和重度 COVID-19 的有效性分别达到 92.1% 和 97.9%。