COVID-19: after infection, children have more antibodies than adults

Infants and young children who were infected with the SARS-CoV-2 virus, which causes COVID-19, have significantly higher levels of antibodies compared to adults. This was indicated by a study led by researchers at the Johns Hopkins Bloomberg School of Public Health in collaboration with the United States Centers for Disease Control and Prevention (CDC).

These results, released on March 22 by JCI Insight, differ from previous research that pointed to a lower antibody response in children. The research is based on samples taken between November 2020 and March 2021 in homes in Maryland, United States, of 682 children and adults who had not yet been vaccinated. Researchers found evidence of antibodies to SARS-CoV-2, indicating that they had already been infected, in 56 people when the study began.

Antibodies directed to the specific zone of the virus that binds to the human receptor, called RBD, were present at much higher levels in children compared to adults: more than 13 times at 0 to 4 years old and almost 9 times more in those aged 5 to 17 years.

In addition, levels of SARS-CoV-2 neutralizing antibodies, which may help predict protection against severe COVID-19 infection, were almost twice as high in children aged 0-4 years compared to adults.

In most households where both children and adults had evidence of antibodies to the infection, those aged 0 to 4 years had the highest levels against RBD and neutralizers, compared to the rest of the family.

This study shows that children, even during their first year of life, have the ability to develop a strong antibody response to SARS-CoV-2 infection, which in some cases exceeds that of adults, said Ruth Karron of Johns Hopkins.

The very young children in the research developed elevated antibody data against the spike protein of SARS-CoV-2, which is the target antigen of COVID-19 vaccines, Karron said.

Another similar study in unvaccinated children looked at the duration of antibodies in children. To analyze this, a team of researchers from Texas Health Houston University, in the US, analyzed data from 218 children across the state from Texas.

And they concluded that children previously infected with COVID-19 develop natural circulating antibodies that last at least seven months, as published in the journal Pediatrics.

For the study, experts analyzed data from children between the ages of five and 19 who enrolled in the Texas CARES survey, which had begun in October 2020, with the aim of assessing the status of antibodies to SARS-CoV-2 over time among a population of adults and children.

The volunteers provided the researchers with three separate blood draws, in samples that were collected prior to vaccination but also during waves of the Delta and Ómicron variants.

To date, researchers have completed three different phases of the study, and so far data showed that while 96% of people infected with coronavirus maintained antibodies until seven months later, more than half (58%) of the sample tested negative for infection-induced antibodies in its third and final measurement. The results do not include the impact of vaccine protection.

“Information on the durability of natural immune responses specific to SARS-CoV-2 in children is important to inform strategies for pediatric vaccination and mitigation of community transmission, both for current variants and for possible future variants,” stressed the authors in the publication of their conclusions.

However, they stressed that “the actual incidence and longitudinal presence of the natural (non-vaccine-induced) antibody response to SARS-CoV-2 infection are not known in the pediatric population due to the high proportion of asymptomatic infection and the prioritization of testing for adults and people with disease serious at the beginning of the pandemic”. However, they emphasized that “this information is important for the field as not all parents can or will choose to vaccinate their children.”

Sarah Messiah is one of the authors of the paper and professor at UTHealth, noting that “this is the first study in the Texas CARES survey that includes data from the three time points of the survey.”

“The findings are important because the information we collected from children infected with COVID-19 did not differ at all if a child was asymptomatic, the severity of symptoms, when they had the virus, if they were at a healthy weight or obesity, or by gender. They were the same for everyone,” said the expert.

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