Covid hospitalizations are rare among children, but still more frequent than for flu, the C.D.C. says.

The number of hospitalizations related to Covid-19 among adolescents in the United States was about three times greater than hospitalizations linked to influenza over three recent flu seasons, according to a study published by the Centers for Disease Control and Prevention on Friday.

The findings run counter to claims that influenza is more threatening to children than Covid-19 is, an argument that has been used in the push to reopen schools, and to question the value of vaccinating adolescents against the coronavirus.

“Much of this suffering can be prevented,” the C.D.C. director, Dr. Rochelle P. Walensky, said in a statement. “Vaccination is our way out of this pandemic.”

Children have a much lower risk overall of Covid-19, compared with adults, but their chances of infection and severe illness are thought to increase with age. Since the start of the pandemic, the rate of hospitalizations among children ages 12 to 17 was 12.5 times lower than among adults. But the rate was higher than that seen in children ages 5 to 11, according to the new report.

The researchers tallied Covid-19 hospitalizations among children ages 12 to 17 from March 1, 2020, to April 24, 2021. The data came from Covid-Net, a population-based surveillance system in 14 states, covering about 10 percent of Americans.

The number of adolescents hospitalized for Covid-19 declined in January and February of this year, but rose again in March and April. Between Jan. 1, 2021, and March 31, 2021, 204 adolescents were likely hospitalized primarily for Covid-19. Most of the children had at least one underlying medical condition, such as obesity, asthma or a neurological disorder.

None of the children died, but about one-third were admitted to the intensive care unit, and 5 percent required invasive mechanical ventilation. Roughly two-thirds of the hospitalized adolescents were Black or Hispanic, reflecting the greater risk posed by the virus to these populations.

The researchers compared the numbers for Covid-19 with hospitalizations for flu in the same age group during the 2017-18, 2018-19 and 2019-20 flu seasons. From Oct. 1, 2020, to April 24, 2021, hospitalization rates for Covid-19 among adolescents were 2.5 to 3.0 times higher than for seasonal flu in previous years.

The rate may have increased this spring because of the more contagious variants of the coronavirus in circulation, as well as school reopenings that brought children together indoors, and looser adherence to precautions like wearing masks and social distancing, the researchers said.

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