Immunogenicity, effectiveness, and safety of COVID-19 vaccines among children and adolescents aged 2–18 years: an updated systematic review and meta-analysis

Background During the coronavirus disease 2019 (COVID-19) pandemic, there is an urgent need for safe and effective COVID-19 vaccines to protect children and adolescents. This study aims to provide scientific evidence and recommendations for the application of COVID-19 vaccines in children and adolescents by analyzing the latest studies. Methods We systematically searched MEDLINE (accessed through PubMed), Embase, and Web of Science from January 1, 2020, to October 8, 2022. Eligible clinical trials, cohort studies, case‒control studies, and cross-sectional studies with extractable data were included in immunogenicity, effectiveness, and safety analyses. According to the heterogeneity, we chose a fixed-effect model (when I 2 ≤ 50) or a random-effects model (when I 2 > 50) to pool effect values. Results A total of 88 articles were included. The seroconversion rates after the first, second, and third doses of the vaccines were 86.10%, 96.52%, and 99.87%, respectively. After the first and second doses, vaccine effectiveness (VE) against severe acute respiratory syndrome coronavirus 2 infection was 42.87% [95% confidence interval (CI) = 27.09%–58.65%] and 63.33% (95% CI = 52.09%–74.56%), respectively. After the first and second doses, VE against COVID-19 was 60.65% (95% CI = 44.80%–76.50%) and 75.77% (95% CI = 63.99%–87.56%), respectively. VE against hospitalization due to COVID-19 after the first and second doses was 72.74% (95% CI = 51.48%–94.01%) and 82.78% (95% CI = 75.78%–89.78%), respectively. The most common adverse events were injection site pain, fatigue/asthenia/tiredness, headache, myalgia/muscle pain, and chills. The incidence rate of myocarditis or pericarditis was 2.42/100,000 people. In addition, the subgroup analysis showed that children aged ≤ 5 years had the lowest incidence of adverse events, and the incidence rate of adverse events was higher for mRNA vaccines than for inactivated vaccines. Conclusions COVID-19 vaccines have good immunogenicity, effectiveness, and safety among children and adolescents. We recommend that children and adolescents be vaccinated as soon as possible to protect them and slow the spread of COVID-19.