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Effectiveness of an Inactivated SARS-CoV-2 Vaccine in Children and Adolescents: A Large-Scale Observational Study
23 Pages Posted: 15 Feb 2022More...
Background: Policymakers urgently need evidence to adequately balance the costs and benefits of mass vaccination against Covid-19 across all age groups, including children and adolescents.
Methods: We used a large prospective national cohort of about two million children and adolescents 6 to 16 years to estimate the effectiveness of an inactivated SARS-CoV-2 vaccine (CoronaVac) in preventing Covid-19 cases, hospitalizations, and admission to intensive care unit (ICU). We compared the risk of individuals treated with a complete primary immunization schedule (two doses, 28 days apart) with the risk of unvaccinated individuals during the follow-up period. The study was conducted in Chile from June 27, 2021, to January 12, 2022. We used inverse probability-weighted survival regression models to estimate hazard ratios of complete immunization over the unvaccinated status, accounting for time-varying vaccination exposure and adjusting for relevant demographic, socioeconomic, and clinical confounders.
Findings: The estimated adjusted vaccine effectiveness for the inactivated SARS-CoV-2 vaccine in children aged 6 to 16 years was 74·5% (95% CI, 73·8–75·2), 91·0% (95% CI, 87·8–93·4), 93·8% (95% CI, 87·8–93·4) for the prevention of Covid-19, hospitalization, and ICU admission, respectively. For the subgroup of children 6-11 years, the vaccine effectiveness was 75·8% (95% CI, 74·7–76·8) for the prevention of Covid-19 and 77·9% (95% CI, 61·5–87·3) for the prevention of hospitalization.
Interpretation: Our results suggest that a complete primary immunization schedule with the inactivated SARS-CoV-2 vaccine provides an effective protection against severe Covid-19 disease for children 6-16 years.
Funding Information: This research was supported by the Agencia Nacional de Investigación y Desarrollo (ANID) Millennium Science Initiative Program MIDAS [NCN17_059] to AJ; Advanced Center for Chronic Diseases (ACCDiS) ANID FONDAP  to RA; and Research Center for Integrated Disaster Risk Management (CIGIDEN) ANID FONDAP  to EU.
Declaration of Interests: The authors declare no conflicts of interest.
Ethics Approval Statement: The research protocol was approved by the Comité Ético Científico Clínica Alemana Universidad del Desarrollo. The study was considered exempt from informed consent, no human health risks were identified. Research analysts belong to the Chilean Ministry of Health; our use of data follows Chilean law 19.628 on personal data protection.
Keywords: SARS-CoV-2, Covid-19, vaccine effectiveness, inactivated SARS-CoV-2 vaccine, mRNA vaccine, pediatric cohort
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