Although not all states report their pediatric hospitalization rates, the data that is available suggests that they have remained essentially steady for months. Nationally, roughly 1 percent of children who are infected with the virus end up hospitalized, and 0.01 percent die, according to the A.A.P. data. Both hospitalization and death rates have declined since last summer.
It is still possible, of course, that Delta could turn out to cause more severe disease in children. Hospitalization rates, which are a lagging indicator, could rise in the weeks and months ahead. And the rare but serious inflammatory syndrome that develops in some children with Covid-19 can take weeks to appear.
“I think time will tell, really,” Dr. Rahman said. “We need at least a month, maybe two months before we get a sense of trends.”
But in the U.K., where Delta swept through the population before the variant became widespread in the United States, experts say they have not seen clear evidence that the variant is making children sicker.
“There was a wave, there were children who became unwell,” said Dr. Elizabeth Whittaker, a pediatric infectious disease and immunology specialist at Imperial College London. “But not in the kind of, ‘Oh, my gosh, this is very different, this is worrying.’”
Whether or not Delta turns out to be more severe, the variant is clearly driving a surge of new infections in both children and adults, especially in areas where vaccine coverage is low. “The rates among children are going up because the rates among unvaccinated family members in their homes are going up,” Dr. Maldonado said.
And more infected children means more hospitalized children. “It’s a numbers game at this point,” Dr. Versalovic said.