Why is COVID-19 less severe in children?

Analyzing nasal swabs taken during the pandemic, a team of researchers from Yale School of Medicine suggested that the persistent presence of other viruses and bacteria may have boosted children's immunity and protected them from the worst effects of COVID-19. The study findings are published in Journal of Experimental Medicine (JEM) ,1 reliable source
High burden of viral and bacterial pathogens impairs nasal innate immunity in children

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SARS-CoV-2 infection in children

Children are generally more susceptible to respiratory infections than adults Such as the common cold, and yet, for unknown reasons, the SARS-CoV-2 virus causes less severe symptoms in children than in adults, resulting in lower rates of hospitalisation and death during the COVID-19 pandemic. The innate immune system provides the first line of defence against viruses and bacteria, producing a range of anti-viral and proinflammatory proteins to prevent infection while the body develops other, more targeted, immune responses such as antibodies. Studies have shown that compared with adults, Innate immune system more active in nasal passages of children and may therefore be better at preventing the early stages of SARS-CoV-2 infection. But the reason for this increased activity is unknown.

“Earlier studies suggested that enhanced nasal innate immunity in children was due to intrinsic biological mechanisms inherent to their age,” says Ellen F. Foxman, MD, associate professor of laboratory medicine and immunobiology at Yale School of Medicine and senior author of the new study. JE Meter study. “But we thought it might also be because of the higher burden of respiratory viruses and bacterial infections in children.”

Common cold may boost children's immunity against SARS-CoV-2

To investigate whether frequent respiratory infections are responsible for increased nasal innate immunity in children, Foxman and colleagues re-analyzed more than 600 nasal swabs originally taken from pediatric patients during the pandemic who were about to undergo elective surgery or emergency room evaluation. Initially tested only for the presence of SARS-CoV-2, Foxman and colleagues re-examined the samples for 19 different respiratory viruses and bacteria, as well as measured the levels of antiviral and inflammatory proteins produced by the innate immune system. The researchers found that many children—even those with no symptoms—were infected with respiratory pathogens other than SARS-CoV-2. This was particularly true for younger children, with nearly 50% of asymptomatic patients under the age of five detected with viruses or infection-causing bacteria

for further investigation Association between respiratory infections and nasal innate immunityFoxman's team compared nasal swabs taken from healthy one-year-old children at both a routine checkup and a follow-up appointment one to two weeks later. More than half of the children tested positive for a respiratory virus at one of their two visits to the pediatrician, indicating that they had either contracted the infection or recovered in the intervening period. In almost every case, the child's innate immune activity was higher at the time they were infected and lower at the time they were virus-free.

“This suggests that the nasal antiviral defenses in young children are not always on high alert, but rather become activated in response to infection with a respiratory virus, even when that virus is not causing symptoms,” Foxman says.

Overall, the study results indicate that the innate immune system is often highly activated in children's nasal passages because they are often infected with relatively benign pathogens, such as the rhinoviruses responsible for the common cold. Foxman speculates that young children are more likely to have infections with common seasonal viruses than adults because they have less immune protection from prior exposure (such as antibodies). However, since SARS-CoV-2 was a new virus to the human population, neither adults nor children had prior protection when the COVID-19 pandemic began. In this case, activation of generalized antiviral defenses in children by other infections may have helped fight the early stages of SARS-CoV-2 infection, leading to less severe outcomes in children than in adults.

“We have identified respiratory viruses and bacteria as key drivers of enhanced nasal innate immunity in children,” says Foxman. “Our results compel further study on how seasonal respiratory viruses and nasal bacteria influence disease severity of COVID-19 and pediatric immune responses in general.”

Reference:

1. High burden of viral and bacterial pathogens compromises nasal innate immunity in children ( https://rupress.org/jem/article/221/9/e20230911/276830/High-burden-of-viruses-and-bacterial-pathobionts)

Source- Eurekalert