COVID-19(45) children(26) SARS-CoV-2(25) pediatric(24) Patient(21) coronavirus disease(21) coronavirus(17) acute respiratory syndrome(16) Infection(16) Coronavirus disease 2019(11) oncology(11) antibody(11) analyzed(10) leukemia(9) hematology(9) patients(9) described(9) Cancer(9) COVID-19 infection(9) pediatrics(8) age(8) Pediatric patient(8) SARS-COV-2 infection(8) IgM and IgG(8) vaccination(7) Cohort(7) patient cohort(7) increased risk(7) outcome(7) nine(7)