key: cord-0788326-c7p0euwn
authors: Yavuz, Sinan; Kesici, Selman; Bayrakci, Benan
title: Physiological advantages of children against COVID‐19
date: 2020-06-26
journal: Acta Paediatr
DOI: 10.1111/apa.15410
sha: 5358a14456cc0f6e01449f482727a1112a2d10b6
doc_id: 788326
cord_uid: c7p0euwn

We read the editorial by Dr. Brodin with great interest, which is discussing why COVID-19 appears to be so mild in children(1). The author discussed the potential theories that could explain why children have a lower incidence and milder clinical manifestations than adults. Additionally to the theories mentioned by the author; we would like to emphasize the differences between the child and adult respiratory systems that potentially protect children from severe COVID-19 disease.

Dear Editor, We read the editorial by Dr Brodin with great interest, which is discussing why COVID-19 appears to be so mild in children. 1 The author discussed the potential theories that could explain why children have a lower incidence and milder clinical manifestations than adults. Additionally to the theories mentioned by the author, we would like to emphasise the differences between the child and adult respiratory systems that potentially protect children from severe COVID-19 disease.

Currently, the pathogenesis of COVID-19 has not been clearly elucidated, but there is evidence that it can enter the human body through angiotensin-converting enzyme 2 (ACE2) on the surfaces of type II alveolar cells. 2 ACE2 is a functional receptor for COVID-19.

ACE2 is widely distributed in the human body; mainly found in the digestive tract, lung, kidney, heart and blood vessels. More than 80% of total ACE2 expression is found in type II alveolar cells. Type II cells express more than 20 other genes closely related to virus replication and transmission and produce surfactant. Newborn has only three million alveoli compared with 500 million alveoli in an adult. It is known that functional residual capacity is smaller and alveolar ventilation is larger in children. So, it can be speculated that less alveolar clearance rate may play a role in viral attachment in adults.

In our opinion, these diverse properties of child respiratory system may also have an impact on the severity of COVID-19 infection.

There are no conflicts of interest in connection with this paper, and the material described is not under publication or consideration for publication elsewhere. 

Why is COVID-19 so mild in children?

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