ACE2 and viral infectious disease: Several hypotheses have been proposed to explain why children are protected from severe outcomes, including differences in the expression of angiotensin-converting enzyme 2 (ACE-2) (Bunyavanich et al., 2020), the receptor for viral entry, a more robust innate immune response in the early phase of the infection, and trained innate immunity related to the protection offered by vaccination and viral infections in childhood (de Candia et al., 2021; Pierce et al., 2021; Vono et al., 2021; Yonker et al., 2021).