Severity of Acute COVID-19 in Children <18 Years Old March 2020 to December 2021

BACKGROUND AND OBJECTIVES: High transmissibility of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Delta variant led to increased coronavirus disease 2019 (COVID-19) cases, but its effect on severe illness among children is less clear. This study evaluated changes in COVID-19 severity from March 1, 2020, to December 30, 2021. METHODS: We examined electronic health record data from encounters that occurred in outpatient and inpatient settings in 9 health systems participating in PEDSnet. The study sample included children aged <18 years with a positive viral test for SARS-CoV-2. Severity was categorized as asymptomatic, mild (symptoms), moderate (moderately severe COVID- 19-related conditions such as gastroenteritis, dehydration, and pneumonia), or severe (unstable COVID-19-related conditions, ICU admission, or mechanical ventilation). RESULTS: The number of patients classified as asymptomatic was 54 948 (66.4%), with 22 303 (26.9%) being mild, 3781 (4.6%) being moderate, and 1766 (2.1%) being severe. In 2021, patients with moderate to severe illness peaked in June (13.5%), declining to December (8.1%). Compared with July 2020 to February 2021, the adjusted odds ratio for moderate to severe illness was highest in June 2021 (adjusted odds ratio, 2.8; 95% confidence interval, 2.2-3.6) and lower in July to December 2021, when the Delta variant predominated. The adjusted odds ratio for moderate to severe illness among children with complex chronic conditions was 4.2 (95% confidence interval, 3.9-4.5). CONCLUSIONS: Although 1 in 16 children infected with the SARS-CoV-2 virus experienced moderate or severe illness, the risk of severe disease did not change with the emergence of the Delta variant, despite its high transmissibility.