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Researchers in Switzerland and Australia have carried out a study to understand why novel coronavirus is less severe in children than adults.
The findings, published in the journal Archives of Disease in Children, stated that parallel changes in how the immune system functions and differences in the endothelium and clotting processes.
The research was conducted by Petra Zimmermann from the University of Fribourg in Switzerland and Nigel Curtis from Murdoch Children’s Research Institute in Victoria, Australia.
“This pattern is strikingly different to that for infection with most other respiratory viruses, for which both the prevalence and severity are higher in children,” said Zimmermann and Curtis.
According to the researchers, the difference in severity is because of various health factors, including Vitamin D levels, expression of ACE2 receptor cells, among others.
For instance, the epithelial expression of ACE2 in lung and nasal tissues increases as a person ages. Furthermore, it has been proposed that in children, ACE2 has a lower binding affinity for SARS-CoV-2, potentially making it more difficult for the virus to enter host cells, the researchers said.
Researchers stated other factors that can drive the severity of the infection in adults. Examples of such factors that might be protective among children range from higher levels of melatonin and differences in gut bacteria (microbiota) to less intense exposure to SARS-CoV-2.
Researchers have proposed that children may have less intense viral exposure than adults, who may be subjected to more exposure in the workplace, or while shopping or traveling.
Role of endothelium
The study suggested that the endothelium in children is less “pre-damaged” than in adults, making them less susceptible to abnormal clotting.
The endothelium is the lining of the interior surface of blood vessels and lymphatic vessels. The endothelium forms an interface between circulating blood or lymph in the lumen and the rest of the vessel wall.
Innate immune system
Children also have more robust innate immune system responses and higher levels of natural killer cells than adults. This innate immune response is the first line of defense in cases of SARS-CoV-2 infection.
Another important factor is adaptive or “trained immunity,” where innate immune cells are reprogrammed following infection to provide immune memory in cases of future infection.
Zimmerman and Curtis believe that overall, the observation that SARS-CoV-2 infection leads to less severe disease in children than in adults is still not well understood.
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