Previous studies have shown that a potent immune response may cause people who become seriously ill or die of Covid-19. A weaker immune response in children may indicate that they clear the virus before it causes severe damage to the body and explains why they are usually spared the disease’s severe symptoms. According to an immunologist at Columbia University in New York, Donna Farber, made for Nature Immunology, children can be infectious for a shorter period. The Dr. and her colleagues analyzed antibodies to 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 children hospitalized with a multisystem inflammatory syndrome, a rare condition that affects some infected children; and 31 infected children who did not have the syndrome. About half of the last group of children showed no symptoms.

The children mainly produced a type of antibody, called IgG, which recognizes the spike protein on the virus’s surface. On the other hand, adults produced several types of antibodies against pico and other viral proteins, and these antibodies were more potent in neutralizing the virus.

The children had “less protective response, but also less range of antibody response,” said Farber. “It is because these children are not being infected so severely.”

However, other experts have recommended caution in interpreting the results because the body’s type of antibodies varies throughout an infection. The immunologist at the Karolinska Institutet in Stockholm, Petter Brodin, says that this study is at risk of comparing apples and oranges.

Other experts warned that the study is too small to conclude how the immune response can vary in children of different ages. According to the immunologist at Rutgers University, Dr. Maria L. Gennaro, it is vital to understand what happens in children and their nature and how they contribute to the spread of the virus in the community.

The researchers were also unable to 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 a good thing,” said Dr. Bhattacharya. “It usually means that something went wrong at the beginning of the response.”

At least one other study suggested that children have a robust innate immune system, designed to fight the many new pathogens they encounter. This first line of defense can eliminate infection early, without the need for other antibodies. Another possibility is that the 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?” Dr. Bhattacharya said. “I think those are both possible.”