Pediatric Infection-Induced SARS-CoV-2 Seroprevalence Increases and Seroprevalence by Type of Clinical Care-September 2021 to February 2022

Background Trends in estimates of US pediatric SARS-CoV-2 infection-induced seroprevalence from commercial laboratory specimens may overrepresent children with frequent health care needs. We examined seroprevalence trends and compared seroprevalence estimates by testing type and diagnostic coding. Methods Cross-sectional convenience samples of residual sera September 2021-February 2022 from 52 US jurisdictions were assayed for infection-induced SARS-CoV-2 antibodies; monthly seroprevalence estimates were calculated by age group. Multivariate logistic analyses compared seroprevalence estimates for specimens associated with International Classification of Diseases-Tenth Revision (ICD-10) codes and laboratory orders indicating well-child care with estimates for other pediatric specimens. Results Infection-induced SARS-CoV-2 seroprevalence increased in each age group, from 30% to 68% (1-4 years), 38% to 77% (5-11 years), and 40% to 74% (12-17 years). On multivariate analysis, patients with well-child ICD-10 codes were seropositive more often than other patients aged 1-17 years (adjusted prevalence ratio [aPR] 1.04; 95% confidence interval [CI], 1.02-1.07); children aged 9-11 years receiving standard lipid screening were seropositive more often than those receiving other laboratory tests (aPR, 1.05; 95% CI, 1.02-1.08). Conclusions Infection-induced seroprevalence more than doubled among children younger than 12 years between September 2021 and February 2022, and increased 85% in adolescents. Differences in seroprevalence by care type did not substantially impact US pediatric seroprevalence estimates. Epidemiologically important differences in infection-induced SARS-CoV-2 antibody seroprevalence estimates were not seen between children receiving well-child care and those with acute or chronic conditions, indicating that care type is not an important source of bias for US pediatric seroprevalence estimates.