The authors were interested in the immune features associated with COVID-19 disease severity in paediatric patients. They collated a case series of 157 patients admitted to Wuhan Children’s Hospital with laboratory-confirmed COVID-19. 38.2% of the children had mild clinical type with pneumonia, 56.1% had moderate disease, 3.8% had severe disease and 1.9% were critically ill. The 148 children with mild or moderate disease had a median age of 84 months, and 59.5% were girls. The most common laboratory abnormalities were increased levels of alanine aminotransferase (ALT, 16.0 U/L), aspartate aminotransferase (AST, 30.0 U/L), creatine kinase MB (CK-MB, 24.0 U/L) and lactate dehydrogenase (LDH, 243.0 U/L), all of which are associated with liver and myocardial injury. Compared with mild cases, the levels of inflammatory cytokines including interleukin 6, tumour necrosis factor α and interferon γ were unchanged, while the level of the immune suppressive interleukin 10 was significantly increased in moderate cases compared with mild cases (3.96 vs. 3.58 pg/mL). There was no difference in the absolute numbers of lymphocytes (including T and B cells) between mild and moderate cases, but moderate cases were associated with a significant decrease in neutrophil levels compared with mild cases (2310/μL vs. 3120/μL). Both immunoglobulin G levels and neutrophil to lymphocyte ratios were negatively associated with biochemical indices related to liver and myocardial injury, while lymphocyte counts, CD4+ T cells and interleukin 10 were positively associated. Therefore systemic inflammation rarely occurred in paediatric patients with COVID-19, in contrast with the lymphopenia and increased inflammatory responses seen in adults.
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