"In addition to public health implications, this population will be important for targeting immunization efforts as SARS-CoV-2 vaccines become available", they said in the study.
The research was unveiled by the medical journal, Jama Pediatrics and published by the American Medical Association.
The paper comes as the administration of United States President Donald Trump is pushing hard for schools and daycare to reopen in order to start the economy. Which means they have just as much of the virus - if not more - present there than adults and older kids. "They also do not represent patients during acute COVID-19 infection or those who are completely asymptomatic with COVID-19".
"I've heard lots of people saying, 'Well, kids aren't susceptible, kids don't get infected.' And this clearly shows that's not true", said Stacey Schultz-Cherry, a virologist at St. Jude Children's Research Hospital to the New York Times. All were diagnosed in March and April. Originally, she tells the Times, "it wasn't even something we had set out to look for".
Heald-Sargent and his team made this conclusion after analyzing samples collected from patients with mild to moderate.
They compared "viral load" in three age groups: children younger than 5 years, kids between 5 and 17 years of age and adults between 18 and 65 years old.
"Having adults model good behavior, having them encourage their children to wash their hands and to wear their mask as much as possible, cleaning high touch areas, being careful with diapers" are all good practices, she said, adding that small children usually want to please their parents. The study, which did not directly compare itolizumab to a placebo or other treatments, has not yet been peer-reviewed.
Children kindergarten-age or younger had viral loads between 10-fold and 100-fold greater amount in their upper respiratory tract.
The researchers cautioned that the study is limited to detection of viral genetic material - its nucleic acid molecule RNA - rather than infectious virus. Their computer models assumed that students with positive tests or with COVID-19 symptoms would be moved to an isolation dormitory. "It's not surprising to find higher viral loads in children".
Scientists have also been turning to other diseases to assess how likely children are to transmit the coronavirus, but evidence is still lacking.
As the coronavirus disease (COVID-19) continues to wreak havoc across the globe, it has been thought that children mostly seemed to be spared by severe illness.
"It's concerning the youngest individuals were the ones with the highest amount of virus", said lead researcher Dr. Taylor Heald-Sargent, a pediatric infectious diseases specialist at Lurie Children's Hospital in Chicago.
The study may highlight the ability of younger children to spread the virus to others, which could help revise current guidelines in containing the spread of the virus.