ACE2 and COVID-19: Some studies reported that the number and function of ACE2 receptors are lower in children than in adults, and lower ACE2 and TMPRSS2 expression in nasal and bronchial epithelial cells in children compared to adult COVID-19 patients was reported (Saheb Sharif-Askari et al., 2020); however, distinctions in the expression of viral entry factors between children and adults are not clear, as only some studies support the hypothesis that fewer ACE2 receptors in children can account for reduced viral entry into the lung (Chou et al., 2022).