Why do kids have milder Covid symptoms than adults? A new study sheds some light

A new study supported by the National Institutes of Health reveals why kids are usually spared from severe Covid symptoms—and the reason may surprise you. 

In the study, when looking at the antibody response of a group of infants who were infected with Covid, researchers found that infants’ immune response is located in their nose, rather than in the blood like adults. And this explains why children have less severe responses, because typically, Covid enters into the human body through the nose or mouth. 

The nose is the perfect place for protective antibodies and an immune response to hang out for children who come in contact with Covid. Children are able to defend against Covid right as it enters their body through their nose before it moves throughout the rest of their body.

The research involved 81 full-term infants and young children whose mothers enrolled in a NIAID-supported cohort study at Cincinnati Children’s during their third trimester of pregnancy, according to the study. 

The mothers had to collect weekly nasal swabs from their infants starting when the babies were two weeks old, and the infants also had regular blood draws starting at 6 weeks old. This was to ensure that scientists could effectively study the children’s immune responses before, during, and after they were exposed to the virus the first time. 

“Fifty-four of the children became infected and had mild COVID-19, while 27 who tested negative through the study period served as matched controls. At the time of infection, the children were 1 month to nearly 4 years old, and half were 9 months or younger,” the study noted. 

The study revealed several things. 

Infants and young kids produce an antibody response that lasts longer than adults, and that antibody response to Covid is different from adults. Children in the study produced protective antibodies at levels that “spiked and remained high” for up to the full observation period—which was 300 days. Typically, adults produce antibodies to the virus at levels that spike initially, then decline after a few weeks.

Additionally, children have more nasal antibody responses than adults (nipping the virus in the bud immediately), and adults have more inflammatory cytokines than children. Cytokines are the proteins that are linked to severe cases and symptoms.

What does this mean for the Covid vaccine? Researchers involved in the study say that it may be possible to devise “vaccine adjuvants” that mimic the immune responses in young children by “stimulating persistently high antibody levels” without causing dangerous excess inflammation in the blood. 

As for Covid vaccines in children, the study said children should still be vaccinated. “Children aged 6 months to 4 years who got COVID-19 vaccines before September 12, 2023, should get one or two doses of updated COVID-19 vaccine, depending on which vaccine and how many doses they previously received. Children aged 6 months to 4 years who have not been vaccinated should get two or three doses of updated COVID-19 vaccine, depending on which vaccine they receive.”