Binding and neutralizing antibody responses to SARS-CoV-2 in very young children exceed those in adults

BACKGROUND. SARS-CoV-2 infections are frequently milder in children than adults, suggesting that immune responses may vary with age. However, information is limited regarding SARS-CoV-2 immune responses in young children. METHODS. We compared receptor binding domain-binding antibody (RBDAb) titers and SARS-CoV-2-neutralizing antibody titers, measured by pseudovirus-neutralizing antibody assay in serum specimens obtained from children aged 0-4 years and 5-17 years and in adults aged 18-62 years at the time of enrollment in a prospective longitudinal household study of SARS-CoV-2 infection. RESULTS. Among 56 seropositive participants at enrollment, children aged 0-4 years had more than 10-fold higher RBOAb titers than adults (416 vs. 31, P < 0.0001) and the highest RBOAb titers in 11 of 12 households with seropositive children and adults. Children aged 0-4 years had only 2-fold higher neutralizing antibody than adults, resulting in higher binding-to-neutralizing antibody ratios compared with adults (2.36 vs. 0.35 for ID50, P = 0.0004). CONCLUSION. These findings suggest that young children mount robust antibody responses to SARS-CoV-2 following community infections. Additionally, these results support using neutralizing antibody to measure the immunogenicity of COVID-19 vaccines in children aged 0-4 years.