A new study out of Northwestern University Feinberg School of Medicine has found that young children in particular carry far more of the coronavirus than adults.

In fact, the research found up to a “100-fold greater amount of SARS-CoV-2 in the upper respiratory tract of young children” under 5 years old. The study, published in JAMA Pediatrics, looked at 145 COVID-19 patients with mild to moderate illness within one week of when their symptoms began. The researchers compared three age groups: young children under 5, children between 5 and 17 years old, and adults 18 to 65 years old. While they found similar amounts of coronavirus present in older children and adults, in children under 5, they found 10 to 100 times more particles in the respiratory tract.

The research was led by Taylor Heald-Sargent, MD, a pediatric infectious diseases expert at the Ann and Robert H. Lurie Children’s Hospital of Chicago. In the report, Heald-Sargent and her team note that children often drive the spread of respiratory and gastrointestinal illnesses—and COVID-19 may be no different.

“It definitely shows that kids do have levels of virus similar to and maybe even higher than adults,” Heald-Sargent told The New York Times. “It wouldn’t be surprising if they were able to shed [the virus]” and spread it to others. (Viral shedding indicates how long someone is releasing contaminated particles. “Evidence suggests that the novel coronavirus is most contagious when symptoms are worse and viral shedding is high,” WebMD notes.)

The research notes that school closures early in the pandemic likely “thwarted larger-scale investigations of schools as a source of community transmission.” In other words, we do not yet know if schools are COVID-19 superspreaders because we shut them down in the first few weeks of the outbreak.

A recent study out of South Korea—published in the CDC’s journal Emerging Infectious Diseases—looked at whether or not children spread COVID-19. Researchers looked at 5,700 people who reported coronavirus symptoms between January 20 to March 27, which is when South Korea closed schools. The findings indicate that those between the ages of 10 and 19 are the most likely to spread the coronavirus in their households.