Researchers from the Columbia university (USA) have conducted an in-depth examination of the antibodies against SARS-CoV-2in children, and surprisingly shows differences in antibodies suggesting that the course of infection and the immune response is different in children and adults, so that most patients children easily eliminate the virus of their bodies.

Therefore, according to the study published in ‘Nature Immunology‘, children and adults produce different types and amounts of antibodies in response to infection with the new coronavirus, SARS-CoV-2, which would explain one of the most striking manifestations of the pandemic: that the most children cope well the virus while older people fight.

“In children, infectious course its alot shorter and probably not as widespread as in adults. Children can clear this virus more efficiently than adults and may not need a strong antibody immune response to clear it, “says Matteo Porotto, associate professor of viral molecular pathogenesis in the Columbia Department of Pediatrics and co-author of the study. with Columbia University immunologist Donna Farber.

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“This is a new infection for everyone, (…) but children are uniquely adapted to seeing pathogens for the first time. That’s what your immune system is designed for. Children have many goal T Naive that can recognize all kinds of new pathogens, while older people rely more on our immune memory. We are not as capable of responding to a new pathogen as children, “says Farber.

Children make less neutralizing antibodies

Among the 47 children in the study, 16 were treated at the Irving Medical Center from Columbia University for multisystem inflammatory syndrome in children (MIS-C) and 31 children of similar ages tested positive for the virus after visiting the medical center for treatment of other conditions. Half of the children without MIS-C had no symptoms of COVID-19. The 32 adults in the study ranged from severely affected patients admitted to the hospital to those with milder illness who recovered at home.

Both groups of children produced the same antibody profilethe study found, which differed from that of adults. Compared to adults, children produce less antibodies against the virus spike protein, which the virus uses to infect human cells. Children’s antibodies had the least neutralizing activity, while all Adults, including 20-year-olds, produced neutralizing antibodies. The sickest adults had the most neutralizing activity.

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Although it may seem counterintuitive that the sickest patients produce antibodies with the highest neutralizing activity, Farber points out that they probably reflects the amount of time that the virus is present in the sickest patients. “There is a connection between the magnitude of your immune response and the magnitude of the infection: the more severe the infection, the more robust the immune response, because you need to have more immune cells and immune reactions to eliminate a higher dose of a pathogen. “, Explain.

Childhood infections are limited

Unlike adults, children also make very few antibodies against a viral protein that is only visible to the immune system after the virus infects human cells. This suggests that in children, infection does not spread much and it doesn’t kill many of your cells.

“Because children clear the natural virus quickly, they do not have a widespread infection and do not need a strong antibody response“Porotto notes. The reduced course of infection in children may mean that they are infectious for a shorter period of time compared to adults and therefore less likely to spread the virus, although researchers did not measure viral load In the kids.

“Current studies in other countries indicate that younger school-age children are not vectors of the new coronavirus, so our data is consistent with those findings,” adds Farber.

Children should respond well to the vaccine

The antibody responses found in children do not suggest that children have a weaker response to a vaccinesay the researchers. Vaccines in development for SARS-CoV-2 contain parts of the virus and do not mimic the normal route of infection.

“Although children do not produce neutralizing antibodies in response to a natural infection with SARS-CoV-2, vaccines are designed to generate a response protective immune in the absence of an infection. Children respond very well to vaccines and I think they will develop good antibody responses neutralizers to a vaccine against SARS-CoV-2, and they will probably be better protected than adults, “warns Farber.

That said, very few vaccine studies are currently enrolling children, and we will need this data to really understand how well vaccines work in children.

What is missing from the adult immune system?

Although the findings suggest that the course of infection in children and adults is different, it is not yet known how children can more easily clear the virus and what the immune system of adults lacks.

Farber, Porotto and their Columbia colleagues are now looking differences in the T cell response (Antibodies are produced by the B cells of the immune system), especially the T cells that reside in the lung.

Children infected with SARS-CoV-2 can also generate a stronger response from the innate immune system, which deploys interferon and cells called macrophages to indiscriminately attack cells infected by pathogens. Previous studies suggest that the innate immune response may be delayed in adults infected with SARS-CoV-2.

“If the innate response is really strong, that can lower the viral load in the lungs, and the antibodies and T cells of the adaptive response have less to clear up,” Farber says. Also, the virus may be less able to infect children’s cells, possibly because children’s cells express less protein that the virus needs to infect human cells.

The Columbia researchers are testing these possibilities with cells from children versus those from adults. “There are still all these topics that we have very little information about. interaction between virus and host is the reason we see so much diversity in the responses to this virus, but we still don’t understand enough about this virus to really determine what leads to severe illness and what leads to mild illness, “they concur.