Multisystem inflammatory syndrome in children (MIS-C) 1 manifests as immune dysregulation after SARS-CoV-2 infection. 2 The syndrome has no pathognomonic features. Thus, the diagnostic criteria of the Royal College of Paediatrics and Child Health (RCPCH), the Centers for Disease Control and Prevention (CDC) and the World Health Org anization (WHO) differ, but they all include fever, evidence of systemic inflammation and involvement of at least 1 organ or system. 3 Our primary objective was to assess initial clinical or laboratory features that predict severe illness in MIS-C. We also sought to explore changes in overall disease severity and cardiac involvement over time as it was the impression of many investigators that severity of MIS-C increased through pandemic waves.

in Canada. COVID-19-related abnormalities in the hematologic characteristics among inpatient children. Results of the PICNIC Registry. ISTH 2021 Congress. https://abstracts.isth.org/abstract/covid-19related-abnormalities-in-the-hematologiccharacteristics-among-inpatient-childrenresults-of-the-picnic-registry/

Age is the most important determinant of COVID-19 severity. Infectious disease severity by age is typically J-shaped, with infants and the elderly carrying a high burden of disease. We report on the comparative disease severity between infants and older children in a multicenter retrospective cohort study of children 0 to 17 years old admitted for acute COVID-19 from February 2020 through May 2021 in 17 pediatric hospitals. We compare clinical and laboratory characteristics and estimate the association between age group and disease severity using ordinal logistic regression. We found that infants comprised one-third of cases, but were admitted for a shorter period (median 3 days IQR 2–5 versus 4 days IQR 2–7), had a lower likelihood to have an increased C-reactive protein, and had half the odds of older children of having severe or critical disease (OR 0.50 (95% confidence interval 0.32–0.78)). Conclusion : When compared to older children, there appeared to be a lower threshold to admit infants but their length of stay was shorter and they had lower odds than older children of progressing to severe or critical disease. What is Known: • A small proportion of children infected with SARS-CoV-2 require hospitalization for acute COVID-19 with a subgroup needing specialized intensive care to treat more severe disease. • For most infectious diseases including viral respiratory tract infections, disease severity by age is J-shaped, with infants having more severe disease compared to older children. What is New: • One-third of admitted children for acute COVID-19 during the first 14 months of the pandemic were infants. • Infants had half the odds of older children of having severe or critical disease. Supplementary information The online version contains supplementary material available at 10.1007/s00431-022-04422-x.