Compared to adults, COVID-19 in childhood has a usually milder course, which may be explained by few factors, such as lower affinity of ACE-receptor to SARS-CoV2, lower expression of ACE-2 gene in nasal epithelium, different interferon and T cell response, lower prevalence of risk comorbidities, protective heterologous effect of live vaccines, and “trained” innate immunity due to higher exposure of respiratory viruses in childhood [29]. This evidence concerns the gene ACE2 and COVID-19.