Distinct Clinical and Laboratory Features of COVID-19 in Children During the Pre-Delta, Delta and Omicron Wave.

BACKGROUND: The SARS-CoV-2 variants of concern exhibit distinct features in terms of transmissibility and virulence. This study compared the clinical characteristics of COVID-19 in children during pre-Delta, Delta and Omicron waves. METHODS: Medical records of 1163 children <19 years of age with COVID-19 admitted to a designated hospital in Seoul, South Korea, were analyzed. Clinical and laboratory findings during the pre-Delta (March 1, 2020, to June 30, 2021; 330 children), Delta (July 1, 2021, to December 31, 2021; 527 children) and Omicron (January 1, 2022, to May 10, 2022; 306 children) waves were compared. RESULTS: Children during the Delta wave were older and had a higher proportion of fever ≥5 days and pneumonia than children during the pre-Delta and Omicron waves. The Omicron wave was characterized by younger age and a higher proportion of fever ≥39.0 °C, febrile seizure and croup. More children <2 years of age and adolescents aged 10 to <19 years experienced neutropenia and lymphopenia, respectively, during the Delta wave. Children aged 2 to <10 years had a higher incidence of leukopenia and lymphopenia during the Omicron wave. CONCLUSIONS: Distinct features of COVID-19 were observed in children during the Delta and Omicron surges. Continuous scrutiny of the manifestations of variants of concern is needed for appropriate public health response and management.

Croup as a Manifestation of SARS-CoV-2 Omicron Variant Infection in Young Children.

Croup is an acute upper respiratory disease primarily caused by the parainfluenza virus. Owing to inflammation and edema of the upper airways, children present with barky cough and stridor, and some may experience respiratory distress. We investigated children aged < 5 years with coronavirus disease 2019 (COVID-19) admitted to two hospitals in Seoul, South Korea, and observed a spike in croup cases during the omicron surge. Among the 569 children admitted from March 1, 2021 to February 25, 2022, 21 children (3.7%) had croup, and the proportion of croup cases was significantly higher during the omicron wave than that during the delta wave (12.4% vs. 1.2%, P < 0.001). With the immediate administration of corticosteroids and epinephrine via nebulizer, the symptoms improved rapidly. During the current omicron surge, careful monitoring of the symptoms of croup in young children is needed for the diagnosis of COVID-19 and its timely management.