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 RBDAb titers than adults (416 vs. 31, P < 0.0001) and the highest RBDAb 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 ID(50), 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. FUNDING: CDC (award 75D30120C08737).