Previous studies have shown that a potent immune response can cause people to become seriously ill or die from Covid-19. A weaker immune response in children may indicate that they eliminate the virus before it causes severe damage to the body and explains why they are generally spared from the severe symptoms of the disease. According to Columbia University immunologist Donna Farber, in a study published in Nature Immunology, children may be infectious for a shorter period. Dr. Farber and her colleagues analyzed antibodies against the coronavirus in four groups of patients: 19 adult convalescent plasma donors who recovered from Covid without being hospitalized; 13 hospitalized adults with acute respiratory distress syndrome resulting from severe Covid; 16 hospitalized children with multisystem inflammatory syndrome, a rare condition affecting some infected children; and 31 infected children who did not present the syndrome. About half of the last group of children showed no symptoms.
The children primarily produced one type of antibody, called IgG, which recognizes the spike protein on the surface of the virus. In contrast, adults produced several types of antibodies against spike and other viral proteins, and these antibodies were more potent in neutralizing the virus.
Children had a “lower protective response, but also a narrower range of antibody response,” said Farber. “It’s because these children are not being infected as severely.”
However, other experts have recommended caution in interpreting the results because the type of antibodies in the body varies throughout an infection. Petter Brodin, an immunologist at the Karolinska Institute in Stockholm, says this study risks comparing apples to oranges.
Other experts warned that the study is too small to conclude how the immune response may vary in children of different ages. According to Rutgers University immunologist Dr. Maria L. Gennaro, it is vital to understand what happens in children, their nature, and how they contribute to the spread of the virus in the community.
The researchers also could not explain why children have a more limited antibody response. Having fewer types of antibodies may seem like a bad thing, but “having a ton of antibodies is not necessarily a marker of something good,” said Dr. Bhattacharya. “It usually means that something went wrong early in the response.”
At least one other study suggested that children have a robust innate immune system designed to combat the many new pathogens they encounter. This first line of defense may eliminate the infection early, without the need for other antibodies. Another possibility is that children have some protection—in the form of immune cells called memory T cells—from previous encounters with common cold coronaviruses. “Is it all innate? Alternatively, could there be some pre-existing memory?” said Dr. Bhattacharya. “I think both are possible.”
VIVIANE FAVER
Journalist
vfaver@gmail.com