Studies have shown that the expression of ACE2 in the nasal epithelium of older children (10–17 years old), adolescents (18–24 years old), and adults (> 25 years old) is higher than that of young children (4–9 years old), which may be one of the reasons why young children are not susceptible to this virus or have relatively mild symptoms after infection [16]. This evidence concerns the gene ACE2 and infection.