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Children infected with the coronavirus produce weaker antibodies and fewer types of them than adults, suggesting that they clear their infection much faster, according to a new study released Thursday.
Other studies have suggested that an overly strong immune response could be the cause of people becoming seriously ill or dying from Covid-19. A weaker immune response in children can paradoxically indicate that they defeat the virus before it has had a chance to wreak havoc in the body and can help explain why children are mostly spared the severe symptoms of Covid, the disease caused by the coronavirus. . It could also show why they are less likely to spread the virus to others.
“They can be contagious for a shorter period,” said Donna Farber, an immunologist at Columbia University in New York who led the study reported in the journal Nature Immunology.
Having weaker and fewer antibodies doesn’t mean babies would be more at risk for re-infection, other experts said.
“You don’t really need a huge, overly robust immune response to maintain protections for any length of time,” said Deepta Bhattacharya, an immunologist at the University of Arizona in Tucson. “I don’t know if I would be particularly concerned that children have a slightly lower antibody response.”
The study looked at the children’s antibody levels at one time and was too small to provide information on how the levels can vary with age. But it may ask questions for some antibody tests that may be missing infected babies.
Dr Farber and her colleagues analyzed coronavirus antibodies in four patient groups: 19 convalescent adult plasma donors who recovered from Covid without being hospitalized; 13 adults admitted to hospital with acute respiratory distress syndrome resulting from severe Covid; 16 children hospitalized with multisystem inflammatory syndrome, the rare condition that affects some infected children; and 31 infected children who did not have the syndrome. About half of this latter group of children did not have any symptoms.
Individuals in each group had antibodies, consistent with other studies showing that the vast majority of people infected with the coronavirus produce a robust immune response.
“This further underlines that this viral infection itself, and the immune response to this virus, is not that different from what we would expect” from any virus, said Petter Brodin, an immunologist at the Karolinska Institutet in Stockholm.
But the range of antibodies differed between children and adults. The children mainly produced a type of antibody, called IgG, which recognizes the spike protein on the surface of the virus. Adults, in contrast, produced different types of antibodies against the spike and other viral proteins, and these antibodies were more potent in neutralizing the virus.
The children had “a less protective response, but they also had a lesser antibody response,” said Dr. Farber. “It’s because those kids don’t get infected so badly.”
Neither group of children had antibodies against a viral protein called nucleocapsid, or N, which is entangled with the genetic material of the virus. Because this protein is found inside the virus and not on its surface, the immune system would see it and make antibodies only if the virus were widely spread in the body, he said.
“You don’t see any of this in children, and this suggests that there is indeed a shortened course of infection if these children become infected,” he explained.
The discovery could undermine the results of tests designed to collect antibodies against the virus’s N protein. Many antibody tests, including those made by Abbott and Roche and offered by Quest Diagnostics and LabCorp, are specific for N antibodies and therefore may be missing children who have successfully cleared the virus. “This is absolutely an interesting implication of that discovery,” said Dr. Brodin.
Lower levels of the virus in the body would also explain why children generally seem to transmit the virus less efficiently than adults.
But experts have urged some caution in interpreting the results because they represent samples taken from people at a single time.
Samples from the most severely affected children and adults were collected within 24-36 hours of hospitalization or intubation for respiratory failure; those of children with mild or no symptoms were archived after medical procedures.
The type of antibodies produced by the body varies over the time of an infection. This was a limitation of this study because the researchers may have compared people at different points of their infection, Dr. Brodin said. “You risk comparing apples and oranges.”
Other experts warned that the study was too small to draw conclusions about how the immune response can vary in children of different ages. The children in the study ranged in age from 3 to 18, with an average age of 11. But some studies have suggested that teens may be at risk for coronavirus as much as adults.
“It is very important to understand what happens in children,” to understand the nature of their disease, but also how they contribute to the spread of the virus in the community, said Dr. Maria L. Gennaro, an immunologist at Rutgers University. But “trying to stratify by age is a bit of a stretch in the analysis,” he said.
The researchers were also unable to explain why the children have a more limited antibody response.
Having fewer types of antibodies may seem like a bad thing, but “having a ton of antibodies isn’t necessarily an indicator of a good thing,” said Dr. Bhattacharya. “Usually it means something went wrong at the beginning of the answer.”
At least one other study has suggested that children have a powerful innate immune system, intended to fight the many new pathogens they encounter, and that this first line of defense can clear the infection early without having to rely on subsequent antibodies.
Another possibility is that children have some protection – in the form of immune cells called memory T cells – from previous encounters with the common cold coronaviruses.
“Is it all innate? Or could there actually be some pre-existing memory? “Dr. Bhattacharya said.” I think both are possible.
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