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Researches are learning how children with COVID-19 present symptoms of the disease. Getty Images
  • New research suggests children can transmit the virus even if they never show symptoms or after symptoms have resolved.
  • It’s widely thought that kids are less likely to get the virus or become seriously ill from it because they have fewer immune receptors for SARS-CoV-2.
  • The data showed kids can carry a higher level of the virus — and be more contagious — regardless of their receptor levels.

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As kids head back to school — whether remote, in-person, or both — a few studies are shedding more light on what we know about children and COVID-19.

This comes as more COVID-19 cases are being reported in children. According to the American Academy of Pediatrics, in August there was a 17 percent increase in COVID-19 cases in just two weeks. The New York Times reported that since May COVID-19 cases in children were up more than 720 percent compared to just 270 percent for all Americans.

New commentary from doctors at Children’s National Hospital published in JAMA Pediatrics suggests that children can transmit the virus even if they never show symptoms or after symptoms have resolved.

Researchers examined 91 children with COVID-19 from 22 hospitals and nonmedical isolation facilities throughout South Korea, testing them, on average, every 3 days.

Of them, 20 never developed symptoms, 47 had unrecognized symptoms before their diagnosis, and 18 did not have symptoms until approximately 2.5 days after diagnosis.

As a result, 42 percent of the children were asymptomatic at the time of diagnosis, and 47 percent of them were presymptomatic and later developed symptoms after about 2.5 days. The other children had no symptoms during their entire illness.

Researchers explained that “These data suggest that 93 percent of the children with COVID-19 could have been missed were it not for Korea’s intensive contact tracing and aggressive diagnostic testing.”

Children in South Korea stayed at hospitals or facilities until they tested negative, a practice that may be less common in the United States.

Symptom duration varied from about 3 days to 3 weeks, the study found. The virus was detectable for about 2.5 weeks in the entire group, but about one-fifth of the asymptomatic and about half of the symptomatic children were still shedding virus at 3 weeks.

Researchers weren’t sure if asymptomatic children were transmitting different quantities of virus than those with symptoms. The study only tested for shedding from the respiratory tract, but other research has found the virus in other bodily fluids.

Another study found children had higher levels of the virus in their airways compared to infected adults hospitalized in intensive care units. The study was published in the Journal of Pediatrics.

Researchers looked at 192 children ages 0 to 22 years of age. Of them, 49 were positive for the virus, and 18 had symptoms of multisystem inflammatory syndrome in children (MIS-C), a rare complication linked to the virus.

“I was surprised by the high levels of virus we found in children of all ages, especially in the first two days of infection,” Dr. Lael Yonker, a pediatric pulmonologist and lead author of the study, said in a statement.

“I was not expecting the viral load to be so high,” she continued. “You think of a hospital, and of all of the precautions taken to treat severely ill adults, but the viral loads of these hospitalized patients are significantly lower than a ‘healthy child’ who is walking around with a high SARS-CoV-2 viral load.”

The higher the viral load, the greater the transmissibility or risk of infection.

Symptoms of COVID-19 such as fever, runny nose, and cough are similar to those of flu and common cold. That can make it more challenging to get an accurate diagnosis of COVID-19, Yonker said.

“Kids are not immune from this infection, and their symptoms don’t correlate with exposure and infection,” added Dr. Alessio Fasano, a pediatric gastroenterologist and author. “During this COVID-19 pandemic, we have mainly screened symptomatic subjects, so we have reached the erroneous conclusion that the vast majority of people infected are adults. However, our results show that kids are not protected against this virus.”

It’s widely thought that kids are less likely to get the virus or become seriously ill from it because they have fewer immune receptors for SARS-CoV-2. But the data showed kids can carry a higher level of the virus — and be more contagious — regardless of their receptor levels.

Knowing this, the authors say that schools shouldn’t rely on temperatures to screen for the virus but use other measures such as social distancing and wearing masks.

A study in JAMA Pediatrics reported on how to estimate the prevalence of virus infection among asymptomatic children based on a larger, more continually maintained database.

Dr. Dylan K. Chan, an ear/nose/throat doctor and study author from University of California, San Francisco, said the tool better gauges how likely it is that a child in a group is infected but not showing symptoms.

His team harnessed data from children across the country who were asymptomatic but tested for reasons other than suspicion of COVID-19.

“It is the closest thing to random testing that we have gotten for a large population of kids,” Chan told Healthline. Previous estimates have come from small studies of randomly tested children, or by using data from confirmed cases.

“Because we had such a large, broad, random sampling, we were able to test how the real numbers we obtained were linked to the much larger JHU [Johns Hopkins University] confirmed cases database,” Chan explained.

Over any given period of time, the percentage of asymptomatic kids that were infected was about equal to the weekly incidence rate (per 1,000 general population). The data can estimate the prevalence of infection by U.S. region with “some confidence,” he said.

“Here in San Francisco, for instance, we can… estimate our current asymptomatic pediatric prevalence at about 1.1 percent,” he said. “Which means that in a class of 22 kids, there is a roughly 22 percent chance that at least one kid has a SARS-CoV-2 infection.”

Still, Chan’s team can’t quantify the risk that an asymptomatic child will infect others, or how the risk level may change with the addition of wearing a mask or improving ventilation.

Knowing all this helps, but we still have a lot to learn, noted Dr. Sonja A. Rasmussen, a professor in pediatrics and epidemiology at University of Florida.

“We know that most children have mild effects or may even be without symptoms,” she said, adding that some can have it severely or die from it. Researchers are learning more about MIS-C, she added.

“We are learning more about transmission of the virus from children to others,” Rasmussen said, citing recent research showing that kids have higher levels of virus than adults, but can still give it to others. “That is of concern because some children might carry the virus, but have mild symptoms or none at all — and could transmit the virus to their teacher, parents, and grandparents, who are at higher risk of severe disease,” she explained.

Rasmussen would like to know more about how to decrease transmission from children to others, among other things.

“We know there are ways in schools to decrease the risk of kids becoming infected, but we don’t have a lot of information on how effective they will be in areas where rates of COVID-19 are high,” she told Healthline.

Other countries have been able to successfully open schools without big outbreaks, but their rates of COVID-19 were much lower than what has been seen in many areas of the United States starting school right now, Rasmussen added.

“The most important thing we can all do right now is to do what we can to get COVID-19 under control in our communities. The risks to COVID-19 transmission in school will be lower if we can get our rates down,” she said, citing measures that can help such as wearing masks, social distancing, and proper hand hygiene.