Vaccine Effectiveness Among 5- to 17-year-old Individuals with Prior SARS-CoV-2 Infection: An EHR-Based Target Trial Emulation Study from the RECOVER Project.

The effectiveness of COVID-19 vaccination in children and adolescents with prior SARS-CoV-2 infection remains unclear, particularly for Omicron subvariants. We evaluated vaccine effectiveness against reinfection with Omicron BA.1/2, BA.4/5, XBB, and later subvariants among 5- to 17-year-olds using data from the RECOVER initiative, a national electronic health record database covering 37 U.S. pediatric institutions. We emulated target trials by age group and variant period, comparing previously infected participants between January 2022 and August 2023. During the BA.1/2 period, vaccination reduced the risk of reinfection, with effectiveness rates of 62% in children and 65% in adolescents. During the BA.4/5 period, protection effectiveness in children was 57%, whereas no statistically significant protection was observed in adolescents. During the XBB or later period, no significant protection was observed in either group. In summary, COVID-19 vaccination provided protection against reinfection during early and mid-Omicron periods in previously infected pediatric populations, but effectiveness declined for later variants.