Why are children less affected by Covid-19?

Children are less susceptible to Covid-19, that’s a fact. Thanks to their young age, and because their body is at the peak of its immunity, viruses have less devastating effects on them. Researchers from Columbia University (United States) have succeeded in identifying why their body’s immune response is better in Covid-19 than that of adults. The results of their study were published in the journal nature immunology November 5, 2020.

One of the most striking findings of the Covid-19 pandemic comes from the age of those infected. If the over 65s are the most at risk, other segments of the population can also suffer from serious forms of this disease, especially if risks such as obesity come to weigh in the balance. Surprisingly, children are doing quite well against the coronavirus.

Fewer antibodies, a sign of a disease that is quickly treated

“In children, the infectious course is much shorter and probably less disseminated than in adults, notes Matteo Porotto, professor of molecular pathogenesis at Columbia University. Children can eliminate this virus more effectively than adults, and they may not need a strong antibody-based immune response to get rid of it..”

To understand this mechanism, the researchers recruited 47 children and 32 adults. Of the children, 16 were treated at Columbia University Medical Center for multisystem inflammatory syndrome (MIS-C), a pathology similar in manifestations to Kawasaki disease. The other 31 children tested positive for Covid-19 after a visit to the medical center; in these children, no trace of MIS-C was found.

Regarding adults, they were all affected by Covid-19, but had different levels of severity. Some of them had to be admitted to hospital while others were able to recover at home.

The two groups of children, although affected by different diseases, nevertheless produced the same antibody profile. In them, the antibodies had less neutralizing activity than those of adults. However, it is adults affected by the severe form of Covid-19 who have developed the most neutralizing antibodies.

If the sickest patients produce the most neutralizing antibodies, according to Donna Farber, immunology and chair of surgical sciences at Columbia University, this reflects the time during which the virus remains in the patient’s body.

Less hold on children’s cells

“There is a connection between the extent of your immune response and the extent of the infection: the more severe the infection, the more robust the immune response, because you need more cells and immune reactions to eliminate a higher dose of a pathogen. Children are particularly suited to seeing pathogens for the first time. This is what their immune system is designed for. Children have lots of naïve T cells that are able to recognize all sorts of new pathogens, while older people rely more on their immunological memory. We are not as capable of reacting to a new pathogen as children are.”

Unlike adults, children produced fewer antibodies responsible for attacking the viral protein of Covid-19. This means that the infection does not spread to them and it does not kill many cells. This reaction also highlights the fact that the infection takes place in them over a shorter period of time than in adults. Finally, it is possible that the virus is less able to infect children’s cells because they express less of the proteins that Covid-19 needs to infect human cells.

“Current studies in other countries indicate that young school-aged children are not vectors of the novel coronavirus, so our data is consistent with these findings.”, concludes Donna Farber.