Ping-Ing Lee, Ya-Li Hu, Po-Yen Chen, Yhu-Chering Huang, Po-Ren Hsueh
Published: 25 February 2020
Available reports to date show that COVID-19 seems to be uncommon in children. Recent data reported from the Chinese Centers for Diseases Control and Prevention indicated that among the 44,672 confirmed cases of COVID-19 as of February 11, 2020, 416 (0.9%) were aged 0–10 years and 549 (1.2%) aged 10–19 years. Exploring the underlying reasons may help understand the pathogenesis of COVID-19.
…several infectious diseases are well known to be less severe in children. The reasons for the relative resistance of children to some infectious diseases remains obscure. It was suggested that maturational changes in the axonal transport system may explain the relative resistance of immature mice to poliovirus-induced paralysis. Other suggested reasons include children having a more active innate immune response, healthier respiratory tracts because they have not been exposed to as much cigarette smoke and air pollution as adults, and fewer underlying disorders. A more vigorous immune response in adults may also explain a detrimental immune response that is associated with acute respiratory distress syndrome.
A difference in the distribution, maturation, and functioning of viral receptors is frequently mentioned as a possible reason of the age-related difference in incidence. The SARS virus, SARS-CoV-2, and human coronavirus-NL63 (HCoV-NL63) all use the angiotensin-converting enzyme-2 (ACE2) as the cell receptor in humans. ACE2 expression in rat lung has been found to dramatically decrease with age. This finding may not be consistent with a relatively low susceptibility of children to COVID-19. However, studies show that ACE2 is involved in protective mechanisms of the lung. It may protect against severe lung injury induced by respiratory virus infection in an experimental mouse model and in pediatric patients. ACE2 also protects against severe acute lung injury that can be triggered by sepsis, acid aspiration, SARS, and lethal avian influenza A H5N1 virus infection.
These intriguing findings suggest that children may really be less susceptible to COVID-19. It is important to elucidate the underlying mechanism that may help to manage COVID-19 patients.
ScienceDirect – DOI: https://doi.org/10.1016/j.jmii.2020.02.011