COVID-19 in children: Heterogeneity within the disease and hypothetical pathogenesis

The disease course of coronavirus disease 2019 (COVID-19) is usually mild and self-limiting in previously healthy children, but they may also develop severe disease. Severe COVID-19 infection is especially observed in very young children or those with underlying comorbidities. Moreover, a multisystem inflammatory syndrome that mimics the Kawasaki disease shock syndrome can develop in children that are genetically predisposed to displaying an overactive immune response to SARS-CoV-2 infection. In this review, we describe the clinical phenotypes of mild and severe COVID-19 and multisystem inflammatory syndrome in children (MIS-C). We also discuss the possible immunobiological mechanisms that may be involved in the protection of children against COVID-19 and the development of multisystem inflammatory syndrome.