The researchers also counted Covid-19 hospital stays in children ages 12 to 17 from March 1, 2020 to April 24, 2021. The data comes from Covid-Net, a population-based surveillance system in 14 states that covers about 10 percent of Americans.

Updated

June 6, 2021, 2:38 p.m. ET

The number of adolescents hospitalized with Covid-19 decreased in January and February of this year, but rose again in March and April. From January 1, 2021 to March 31, 204 young people are expected to have been hospitalized mainly for Covid-19. Most children had at least one underlying medical condition, such as obesity, asthma, or a neurological disorder.

The rate could have increased this spring due to the more contagious variants of the coronavirus floating around, as well as the reopening of schools that brought children together indoors and looser adherence to precautions like wearing masks and social distancing, the researchers said .

None of the children died, but about a third were admitted to intensive care and 5 percent required invasive mechanical ventilation. About two-thirds of adolescents admitted to the hospital were Black or Hispanic American, reflecting the greater risk the virus poses to these populations.

The researchers compared the numbers for Covid-19 to hospital admissions for flu in the same age group during the 2017-18, 2018-19, and 2019-20 flu seasons. From October 1, 2020 to April 24, 2021, adolescent hospital admission rates for Covid-19 were 2.5 to three times the rate of seasonal flu in previous years.

The data adds urgency to the drive to get more teenagers vaccinated, said Dr. Walensky, who added that she was “deeply concerned” with the numbers.

The Food and Drug Administration approved the Pfizer BioNTech coronavirus vaccine for children ages 12 to 15 on May 12. The vaccine was approved for all elderly people in December.