A small study involving 108 participants — 57 children and 51 adults — found that compared with adults, a higher proportion of children did not produce antibodies in response to SARS-CoV-2 infection (seroconversion). All the 108 participants were either asymptomatic or had only mild symptoms. The lack of antibodies in children becomes particularly stark as both adults and children had comparable viral load.
The study was carried out between May 10 and October 28, 2020 at the Royal Children’s Hospital, Melbourne, Australia. The study looked at the ability of adults and children to produce antibodies when infected with the Wuhan strain of the virus. Whether children would exhibit the same characteristics in the case of the Delta and Omicron variants, where people tend to have far higher viral loads, is not known.
The study recruited children and adults infected with SARS-CoV-2 and their household members, and samples were collected from the throat and nose to detect the virus; blood samples were collected to measure humoral responses.
The results were published in the journal JAMA Network Open.
Using three serological assays, the team of researchers led by Paul V. Licciardi from the Royal Children’s Hospital found that only 20 of 54 children produced antibodies on being infected, compared with 32 of 42 adults. This was despite the viral load being comparable. The mean cycle threshold (Ct) value for adults was 24.1 while it was 28.5 in the case of children. The smaller the Ct value, the higher is the viral load. However, the researchers say that when the Ct value was less than 26, both adults — 10 of 11 (90.9%) — and children — 12 of 15 (80%) developed antibodies.
“The findings of this cohort study suggest that among patients with mild COVID-19, children may be less likely to have seroconversion than adults despite similar viral loads. This finding has implications for future protection after SARS-CoV-2 infection in children and for interpretation of serosurveys that involve children,” they write.
One reason why 34 children did not develop antibodies despite being infected could be because children have been found to mount a “stronger and faster response” to infection than adults. That would mean that children are able to clear the virus so quickly that the immune system is not triggered to produce antibodies against the virus. So in the absence of antibodies, it is not clear if these children would be protected against reinfection.
The authors found that a higher proportion of adults who did not develop antibodies were asymptomatic — four of 10 (40%). In contrast, adults who had symptoms had greater possibility of developing antibodies. In the case of children, a higher proportion of children who had antibodies did not have any symptoms on infection compared with children who did not develop antibodies. “This outcome suggests that the host humoral response to SARS-CoV-2 infection in children is different in adults despite similar viral loads and exposure to circulating virus variants,” they write.
One reason why children are able to clear the virus without even producing antibodies may be because unlike adults, children have a more robust innate and/or mucosal immune response to the virus. The faster clearance of the virus by children could be again because children have a robust innate immune response than adults. But the authors were not able to confirm these statements in the study.
It was previously shown that adults who did not have antibodies were 80% more susceptible to getting reinfected compared with adults who developed antibodies. Even when adults developed antibodies, the risk of reinfection was higher when the level of antibodies was low. But even antibody levels were low, adults who were reinfected had lower viral load than adults who did not have antibodies and got reinfected.
“Therefore, a lack of seroconversion [lack of antibodies] may result in a higher susceptibility to reinfection. This hypothesis may have important implications on the transmission of SARS-CoV-2 in the community and the public health response,” they write.
