Children infected with the coronavirus produce weaker antibodies and fewer types than adults, suggesting they clear their infection much faster, according to a new study released Thursday.
Other studies have suggested that too strong an immune response may be to blame in people who become seriously ill or die from Covid-19. A weaker immune response in children may ironically indicate that they are defeating the virus before it has had a chance to wreak havoc on the body, and may help explain why children are usually spared severe symptoms. of Covid, the disease caused by the coronavirus. It can also show why they are less likely to spread the virus to others.
“They can be infectious for a shorter period of time,” said Donna Farber, an immunologist at Columbia University in New York City who led the study reported in the journal Nature Immunology.
Having weaker and fewer antibodies doesn’t mean children would be at greater risk for re-infections, other experts have said.
“You don’t really need a huge, overly robust immune response to maintain the protections over a period of time,” said Deepta Bhattacharya, an immunologist at the University of Arizona at Tucson. “I don’t know if I would be particularly worried about children having a slightly lower antibody response.”
The study looked at children’s antibody levels at one point in time and was too small to provide information on how the levels may vary with age. But that could pose questions for some antibody tests that infected children might miss.
Dr Farber and his colleagues analyzed antibodies to the coronavirus in four groups of patients: 19 convalescent adult plasma donors who had recovered from Covid without being hospitalized; 13 adults hospitalized with acute respiratory distress syndrome resulting from severe Covid; 16 children hospitalized for multi-system inflammatory syndrome, a rare disease affecting some infected children; and 31 infected children who did not have the syndrome. About half of this latter group of children had no symptoms.
Individuals in each group had antibodies, which is consistent with other studies showing that the vast majority of people infected with the coronavirus develop a robust immune response.
“It further emphasizes that this viral infection itself, and the immune response to this virus, is not that different from what one would expect” from any virus, said Petter Brodin, immunologist at the Karolinska Institutet in Stockholm.
But the range of antibodies differs between children and adults. The children mainly made a type of antibody called IgG, which recognizes the spike protein on the surface of the virus. Adults, on the other hand, made several types of antibodies against the peak and other viral proteins, and these antibodies were more powerful at neutralizing the virus.
The children had “less of a protective response, but they also had less of an antibody response,” said Dr. Farber. “It’s because these kids just aren’t that badly infected.”
Neither group of children had antibodies against a viral protein called a nucleocapsid, or N, which is entangled with the genetic material of the virus. Because this protein is found in the virus and not on its surface, the immune system would only see it and make antibodies if the virus were widely disseminated in the body, she said.
“You really don’t see any of that in children, and it suggests that the course of the infection is really reduced if these children are infected,” she explained.
This finding could affect the results of tests designed to detect antibodies to the virus’ N protein. Many antibody tests, including those performed by Abbott and Roche and offered by Quest Diagnostics and LabCorp, are specific for N antibodies and therefore may miss children who have successfully cleared the virus. “It’s absolutely an interesting implication of this discovery,” said Dr. Brodin.
Lower levels of the virus in the body would also explain why children generally seem to transmit the virus less effectively than adults.
But experts called for some caution in interpreting the results, as they represent samples taken from people at one point in time.
Samples of the most severely affected children and adults were collected within 24 to 36 hours of admission or intubation for respiratory failure; those of children with mild or no symptoms were banked after medical procedures.
The type of antibodies produced by the body varies over the time of an infection. That was a limitation of this study because the researchers may have compared people at different times during their infection, Dr Brodin said. “You might be comparing apples and oranges.”
Other experts have warned that the study was too small to draw conclusions about how the immune response may vary in children of different ages. The children in the study were aged 3 to 18, with a median age of 11. But some studies have suggested that adolescents may be just as exposed to the coronavirus as adults.
“It is very important to understand what is happening 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, immunologist at the ‘Rutgers University. But “trying to stratify by age is a bit of a stretch in the analysis,” she says.
The researchers were also unable to explain why children have a more limited antibody response.
Having fewer types of antibodies might sound like a bad thing, but “having a ton of antibodies isn’t necessarily a marker of a good thing,” Dr Bhattacharya said. “Usually it means something went wrong at the start of the response.”
At least one other study has suggested that children have strong innate immune systems, designed to fight off the many new pathogens they encounter, and that this first line of defense can clear infection early without needing to resort to subsequent antibodies.
Another possibility is that children may have some protection – in the form of immune cells called memory T cells – from previous encounters with common cold coronaviruses.
“Is everything innate?” Or could there be preexisting memory? Said Dr Bhattacharya. “I think both are possible.”