Estimated SARS-CoV-2 Seroprevalence Among Children: United States, September 2021 to December 2022

BACKGROUND Studying seroprevalence, the prevalence of SARS-CoV-2 antibodies in blood, produces more reliable estimates of infection burden compared with diagnosed cases. In this analysis, United States Nationwide Commercial Laboratory Seroprevalence Study data are used to calculate pediatric seroprevalence trends and their correlation with state-level vaccination. METHODS We tested SARS-CoV-2 antibodies residual serum specimens from pediatric patients during September 2021 to December 2022 for (1) presence of antinucleocapsid (anti-N; infection-induced) antibodies and (2) semiquantitative anti–spike protein (anti-S; vaccination- and infection-induced) immunoglobulin G antibody concentrations. Seroprevalence trends and antibody concentrations by age group over time were evaluated. State-level correlations were calculated between geometric mean concentrations and vaccination data. RESULTS By December 2022, more than 90% of children older than 2 years showed evidence of SARS-CoV-2 infection. In contrast, seroprevalence in infants younger than 1 year fluctuated around 60% from February 2022 on. Older age groups generally exhibited higher anti-N seroprevalence and higher anti-S antibody concentrations. A positive correlation was observed between state-level geometric mean antibody concentration and vaccination rates for children aged 5 to 11 and 12 to 17 years, but not for those aged 6 months to 4 years. CONCLUSION Between September 2021 and November/December 2022, anti-N seroprevalence increased across all age groups except for children younger than 1 year. Seropositivity among these infants remained around 60%. Furthermore, the lowest anti-S concentrations were found in children aged 6 months to 4 years. Given that young children had the lowest seroprevalence, vaccination of those who are pregnant and eligible young children could increase protection through generating an increase in antibody titers.