The new coronavirus has infected nearly 90,000 people, and more than 3,000 have died. But relatively few children appear to have developed severe symptoms so far, according to available data.

“Disease in children appears to be relatively rare and mild,” with those under 19 years making up only 2.4 percent of the total cases, according to a report published Feb. 28 by the World Health Organization.

So why aren’t more children getting sick?

“My strong, educated guess is that younger people are getting infected, but they get the relatively milder disease,” Dr. Malik Peiris, chief of virology at the University of Hong Kong, said last month. Dr. Peiris has developed a diagnostic test for the new coronavirus.

The numbers so far support that theory: According to the W.H.O., only 2.5 percent of those under 19 have developed severe disease and only 0.2 percent had critical disease. There have been no deaths recorded in children under 9.