Differences in the immune system and a better health of the blood vessels were among the factors that protect children from serious diseases COVID-19, according to a new review.
A large amount of global COVID-19 literature has been reviewed and published in the Archives of Disease in Childhood by experts from the Murdoch Children’s Research Institute (MCRI), the University of Melbourne and the University of Friborg to unravel the reasons for age differences. in severity and symptoms of COVID-19.
MCRI and University of Melbourne professor Nigel Curtis said that although a number of hypotheses provide potential explanations for why adults are at higher risk and that children are protected from serious illness and death due to COVID-19, most do not why COVID-19 severity does not rise steeply. after the age of 60–70 years.
Professor Curtis said that in stark contrast to other respiratory viruses, serious illness and death due to COVID-19 were relatively rare in children.
“Most children with COVID-19 have no or only mild symptoms, mostly fever, cough, sore throat and changes in sense of smell or taste,” he said. “Even children with the usual risk factors for serious infections, such as immunosuppression, are not at high risk for severe COVID-19 disease.”
Professor Curtis said that the damage to the thin layer of endothelial cells that feed various organs, especially the blood vessels, heart and lymph vessels, increased with age and that there was a link between conditions affecting these cells and severe COVID-19.
‘We know that pre-existing vascular damage plays an important role in the severity of COVID-19 and can lead to blood clots, which can cause strokes and heart attacks. “COVID-19 can infect these endothelial cells and cause blood vessel inflammation,” he said.
“The endothelium in children suffered much less damage than in adults and their clotting system is also different, making children less prone to abnormal blood clotting.”
Professor Curtis said that diseases associated with chronic inflammation that develop with old age, including diabetes and obesity, are also associated with severe COVID-19.
He said more recent vaccinations with live vaccines, such as the MMR vaccine against measles, mumps and rubella, which could boost the immune system, could play a role in protecting children.
Dr Petra Zimmermann from the University of Friborg said there are other important differences in the immune system between children and adults.
“Children have a stronger innate immune response, which defends the first line against COVID-19,” she said.
Another important factor is ‘trained immunity’ which replenishes innate immune cells after mild infections and vaccinations, leading to a kind of ‘innate immune memory’.
‘Children infected with COVID-19 often have co-infections with other viruses. Recurrent viral infections can lead to improved trained immunity, which can make children more effective at clearing COVID-19. ”
Dr. Zimmermann said that different levels of microbiota (bacteria and other germs) in the throat, nose, lung and stomach also affect the susceptibility to COVID-19.
“The microbiota plays an important role in regulating immunity, inflammation and in the defense against disease,” she said. “Children are more likely to have viruses and bacteria, especially in the nose, where these insects can restrict the growth of COVID-19.”
Dr. Zimmermann said that the vitamin D level, with its anti-inflammatory properties, was usually also higher in children.
“The overlap between risk factors for severe COVID-19 and vitamin D deficiency, including obesity, chronic kidney disease and black or Asian origin, suggests that vitamin D supplementation may play a role in the prevention or treatment of COVID-19,” she said. said.
“In many countries, vitamin D is regularly supplemented in infants younger than one year and in some countries even up to three years.”
Professor Curtis said that understanding the underlying age-related differences in the severity of COVID-19 provides important insights and opportunities for the prevention and treatment of EARS-CoV-2 infections.
MCRI COVID-19 ongoing research project highlights:
- BRACE test to test the BCG vaccine to see if it trains the ‘innate’ immune system of frontline health workers to reduce the severity of COVID-19. Australian recruitment has been completed, and the team is now recruiting in the UK, the Netherlands, Spain and Brazil.
- COVID Immune study investigating COVID-19 effects on children’s immune systems. Study whether some children are more vulnerable to COVID-19 due to differences in their immune system and how long immunity lasts.
- Age-specific blood coagulation study examining the biological factors underlying viral interaction with the coagulation system and the differences between adults and children. Studies can help identify drug targets that alleviate the progression of disease in adults toward children.
- Several studies examining the differences in immune systems of children and their parents when a family member is infected with COVID-19. The underlying differences between children’s and adults’ immune responses to the virus have yet to be determined.
Reference: “Why is COVID-19 less serious in children? A Review of the Proposed Mechanisms Underlying the Age-Related Difference in Severity of SARS-CoV-2 Infections “by Petra Zimmermann and Nigel Curtis, December 1, 2020, Archives of childhood diseases.