Compared with adults, children tend to have lower incidence rate, hospitalization rate, and mortality rate of coronavirus disease 2019 (COVID-19), while the cause of such age-based differences in disease severity remains unclear. An investigation of pathogenesis in children may help to analyze the therapies for the high-risk population. Human angiotensin-converting enzyme Ⅱ is the main receptor of severe acute respiratory syndrome coronavirus 2 and can limit pulmonary capillary leakage and inflammation mediated by angiotensin 2 and exert a protective effect against acute lung injury. Its expression decreases with age. Regular vaccination and frequent upper respiratory virus infection in children can lead to regular immune activation, and its combination with strong innate immunity can help to achieve virus clearance in the early stage of infection in children with COVID-19. Meanwhile, there are strong regeneration and repair abilities of alveolar epithelial cells in children, which may help with the early recovery of infection. In addition, risk factors, such as underlying cardiopulmonary diseases, obesity, and smoking, are relatively uncommon in children. Social factors, including home quarantine and timely closure of schools, may help to reduce the infection rate in children. However, children with immunodeficiency are a high-risk population and should be closely monitored. Further studies are needed to investigate the immune and protection mechanisms against COVID-19 in children.
儿童中新型冠状病毒肺炎（COVID-19）的发生率、住院率和病死率均较成人低，而这种基于年龄的病情程度差异原因尚不明确，探讨儿童发病机制可帮助分析针对高危人群的治疗方法。人血管紧张素转化酶Ⅱ（ACE-2）是新型冠状病毒的主要受体，可限制血管紧张素2介导的肺毛细血管渗漏和炎症，对急性肺损伤具有保护作用，其表达随年龄增长而降低。儿童期定期的疫苗接种及较频繁的上呼吸道病毒感染导致规律的免疫激活，结合其强大的固有免疫系统功能，有助于COVID-19患儿感染早期的病毒清除。同时，儿童肺泡上皮细胞的再生和修复能力较强，有助于感染的早期恢复。另一方面，心肺基础疾病、肥胖和吸烟等危险因素在儿童中相对较少。居家隔离政策、学校及时关闭等社会因素对降低儿童感染率也起到保护作用。但是，伴有其他疾病如免疫缺陷的儿童可能属于高危人群，需给予密切关注。针对儿童COVID-19的免疫和保护机制也需要进一步研究。