Children have accounted for a very small percentage of the more than 200,000 deaths linked to the novel coronavirus in the United States so far—and according to a new study, a key difference may explain why children are not as severely affected by the virus as adults.

Children comprise small percentage of US coronavirus deaths

According to statistics compiled by the American Academy of Pediatrics (AAP) and the Children's Hospital Association, as of Sept. 10, states had reported a total of 105 deaths among people infected with the coronavirus who were under the age of 20. The data showed there were 18 states that hadn't reported a single death among a person infected with the coronavirus who was younger than 20.

Separately, CDC's Covid-19 tracker, which currently includes data spanning through Sept. 28, shows that officials have reported a total of 92 deaths among people under the age of 18 who were infected with the coronavirus. Those 92 deaths comprise 0.06% of the 146,643 total deaths for which age group data was available that CDC has tallied on its site.

Why aren't children hit by the coronavirus as hard as adults?

A new study published last week in Science Translational Medicine may shed some light as to why children infected with the coronavirus are not as likely to die from the pathogen as adults.

For the study, researchers observed the immune responses to the novel coronavirus in 60 adults and compared them with the immune responses observed in 65 people younger than 24, whom the study classified as children. The researchers reported that 20 of the patients included in the study were children who had developed multisystem inflammatory syndrome (MIS-C), which is a rare and potentially fatal condition that has been associated with the new coronavirus. All of the patients involved in the study had been hospitalized at Montefiore Medical Center between March 13 and May 17.

The researchers found that, in general, the children included in the study were affected by the virus only mildly when compared with the adult patients. For example, the researchers reported that just five of the children required ventilation, compared with 22 of the adults. In addition, two of the children died, compared with 17 of the adults.

The researchers concluded that the likely reason children were less affected by the coronavirus was because of the way their immune systems responded to the pathogen.

When an immune system comes into contact with an unknown pathogen, an innate immune response is triggered in which the body quickly responds to eradicate the foreign substance, the New York Times reports. And, as the Times reports, because children more often encounter pathogens unknown to their immune systems, their innate immune responses are fast and strong.

In comparison, as people grow older, their bodies develop a more specialized immune response system that remembers previously encountered pathogens. As a result, the innate immune response fades, the Times reports.

The researchers theorized that, because the new coronavirus was never before encountered by anyone, individuals with weaker innate immune response systems are more vulnerable to the virus. They said their research supports that theory, as they found that the children in the study showed higher levels of two immune molecules, interleukin 17A and interferon gamma, when compared with the adult participants.

Betsy Herold, a pediatric infectious disease expert at Albert Einstein College of Medicine who led the study, said, "We think that is protecting these younger children, particularly from severe respiratory disease, because that's really the major difference between the adults and the kids."

'We will eventually age out of this virus'

Some experts said the researchers' results should be interpreted with caution, because although they thought the study was well done, they also thought the researchers enrolled patients who were too far along in their coronavirus infections for the results to be conclusive.

Akiko Iwasaki, an immunologist at Yale University, explained that innate immune responses occur hours after an individual is exposed to a pathogen and, typically, patients don't seek hospital care for Covid-19 symptoms until around a week after they've been infected with the novel coronavirus. At that point, it's too late to be able to determine how the innate immune system responded to the virus, Iwasaki said. "By the time people are sick, it's way past that time point."

Michael Mina, a pediatric immunologist at the Harvard T.H. Chan School of Epidemiology, said the results suggest that, if the new coronavirus becomes endemic (similar to other coronaviruses that cause the common cold), children eventually could develop an immune defense strong enough that they won't ever experience any of the issues adults currently are experiencing with the novel coronavirus.

That means "[w]e will eventually age out of this virus," Mina said (Mandavilli, New York Times, 9/25; Owens, "Vitals," Axios, 9/28; Bernstein, Washington Post, 9/25).