Pediatric SARS-CoV-2 Incidence in California by Vaccination Status, December 2021 to April 2023

OBJECTIVE This study aimed to provide evidence on trends related to the effects of COVID-19 vaccines (BNT162b2 and mRNA-1273) among children and adolescents in California during December 2021 through April 2023. METHODS We used a surveillance cohort study design to compare case and hospitalization incidence rate ratios (IRRs) between vaccinated and unvaccinated children and adolescents considering age, dose received, and time since vaccination. We evaluated the Omicron BA.1/2 predominant period and the time from which vaccines became available to 1-to-4-year-old children through when the administration of original strain monovalent doses was discontinued. RESULTS Across all age groups and time periods, vaccinated children were less likely to be hospitalized than unvaccinated children. For all but the youngest age group, vaccinated children were also less likely to have a documented COVID-19 infection. IRRs for cases who received any messenger RNA vaccine primary series compared to unvaccinated children ranged from 1.13 (95% CI, 0.82–1.55) for those aged 1 to 4 years to 0.21 (95% CI, 0.19–0.23) for those aged 12 to 17 years. Hospitalization IRRs ranged from 0.33 (95% CI, 0.16–0.65) for those aged 1 to 4 years to 0.17 (95% CI, 0.13–0.21) for those aged 12 to 17 years. CONCLUSION California surveillance data indicates that receipt of a messenger RNA vaccine was associated with reduced rates of COVID-19 infection and hospitalization across all childhood age groups. Although reductions in protection against infection appeared to be attenuated among the youngest age group, protection against hospitalization remained high for this population. Administration of the COVID-19 vaccine is a valuable tool for reducing COVID-19–associated morbidity in children and adolescents.