The findings, published in JAMA Pediatrics, suggest that the vast majority of infected children appear healthy but still may spread the virus to others. The study is hardly the final word: Research into asymptomatic children has been unfolding rapidly, some studies have been reconsidered, and it still is not clear to scientists how often they may transmit the virus and under what circumstances.
The new study is short on details, and does not indicate whether the virus the children shed is alive and capable of infecting others, or whether older children are more contagious than younger ones.
The researchers in South Korea followed 91 children under age 19 — with a median age of 11 — at 20 hospitals and two isolation facilities between Feb. 18 and March 31. They tested the children’s nose, throat and sputum every three days on average. (Anyone in South Korea who tests positive is sent to a hospital or isolation center.)
Twenty children, or 22 percent, remained symptom-free throughout. In the other children, the symptoms spanned a wide range, from lack of smell or taste to diarrhea, cough, runny nose and fever — “not specific enough for Covid-19 to prompt diagnostic testing or anticipate disease severity,” the researchers wrote. Only two children were sick enough to need oxygen.
Of the children with obvious signs of illness, only six had shown symptoms at the time of diagnosis; 18 developed symptoms later. The remaining 47 had unrecognized symptoms before being diagnosed — which is noteworthy given the tight surveillance in South Korea, the researchers said.
Asymptomatic children continued to test positive for 14 days after diagnosis on average, compared with 19 days in children with symptoms. But the researchers did not try to grow the virus to confirm that the tests were not just picking up remnants of dead virus.
Overall, the findings suggest that screening for symptoms is likely to miss the vast majority of infected children who can silently spread it to others. In their study, 93 percent of the children could have been missed were it not for “intensive contact tracing and aggressive diagnostic testing,” the researchers reported.