Assays include SARS-CoV-2 S1/S2 immunoglobulin G (DiaSorin), an antibody enzyme-linked immunosorbent assay (ELISA) (Beijing Wantai Biological Pharmacy Enterprise Co, Ltd [Wantai]), and an in-house ELISA. Immunoglobulin G SARS-CoV-2 antibody levels are expressed as means; error bars indicate 95% CIs. Acute levels were measured at a median of 7-12 (IQR, 4-13) days in 14 children and 17 adults. Convalescent levels were measured at a median of 41 (IQR, 31-49) days in 57 children and 51 adults. AU indicates assay units.