Earlier studies have suggested that (1) children's immune systems might have been trained by vaccinations or other viral infections resulting in robust innate immune responses upon reinfection with the same or unrelated organisms38, 39; (2) children might have lower but increasing density of angiotensin‐converting enzyme 2, the primary receptor target for SARS‐CoV‐2 virus in the respiratory tract38, 39; and (3) adults might experience immunosenescent cells as they advance in age, which could contribute to poor immune responses.38, 39. Here, ACE2 is linked to viral infectious disease.