Low severity of COVID-19 in children, causes and hypotheses
Low severity of COVID-19 in children, causes and hypotheses
Aida Mofazzal Jahromi,1,*Dorsa Gharehghooni,2Soha Azizi,3Rahil Mosallanejad,4Amir Abdoli,5
1. Student research committee, Jahrom University of Medical Sciences, Jahrom, Iran 2. Student research committee, Jahrom University of Medical Sciences, Jahrom, Iran 3. Student research committee, Jahrom University of Medical Sciences, Jahrom, Iran 4. Student research committee, Jahrom University of Medical Sciences, Jahrom, Iran 5. Zoonoses Research Center, Jahrom University of Medical Sciences, Jahrom, Iran
Introduction: In mid-December 2019, severe acute respiratory syndrome (SARS) caused by Coronavirus 2 spread worldwide. Fortunately, most children are asymptomatic or have mild disease and much lower mortality compared to adults. Here, we review Why does the coronavirus causes mild COVID-19 infection in children?
Methods: A systematic search was performed in four databases, including Scopus, PubMed, Science Direct, and ProQuest, to find original articles from 2021 using three main keywords such as COVID-19, mild symptoms, and children. Then, 297 studies were screened in 3 stages, and finally, thirty-two articles that met the eligibility criteria were selected.
Results: Based on the literature review, several factors were found that could explain the different severity of COVID-19 in adults and children. There are two types of angiotensin-converting enzyme 2 (ACE-2) in the body: soluble and in the membrane. ACE inhibitors and underlying disease in adults, by increasing the expression of ACE-2 membrane form, caused the virus to enter the cells more easily. Further expression of soluble ACE-2 in children acts as a neutralizing antibody and plays a protective role against COVID-19. ACE degenerates and inactivate bradykinin, that’s more common in children, therefore symptoms like dry cough, decrease in oxygen saturation, and increased vascular permeability is reduced. Another pathophysiological mechanism of COVID-19 is damage to endothelial cells with SARS-CoV-2 penetration and subsequent inflammation and the creation of a prothrombotic environment that causes increased inflammation and clotting. Because children have healthy vasculature and less endothelial damage, they show milder symptoms. The age-related decline in ciliary cell function facilitates the passage of viruses into the lower respiratory tract. Increased ability of children to repair their lungs after infection, adult thymus atrophy and decreased T cells, and increased sex hormones in adults are other reasons for the lower severity of the disease in children.
Conclusion: According to our conclusion, the most frequent hypotheses and reasons for the age-related difference in the occurrence of SARS-CoV-2 is the difference in the number of ACE2 receptors, and endothelial system physiology. Although the clinical manifestations of COVID-19 in children are less severe than adults, the disease may progress in them and these mild symptoms should not be ignored in them. It should also be emphasized that although children have mild symptoms, they are important vectors of the disease, so children vaccination is considered as a key COVID-19 pandemic-prevention strategy.