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Citing increased hospitalization rates of teenagers with covid-19 in March and April, Centers for Disease Control and Prevention Director Rochelle Walensky urged parents to vaccinate their teens to protect them from an illness that can be severe even among young people.

“I am deeply concerned by the numbers of hospitalized adolescents and saddened to see the numbers of adolescents who required treatment in intensive care units or mechanical ventilation,” Walensky said in a statement that was released Friday alongside a new study looking at trends in hospitalization among adolescents with the disease.

“Much of this suffering can be prevented,” Walensky added, urging “parents, relatives and close friends to join me and talk with teens” about the importance of prevention strategies and to encourage vaccination.

The study showed that nearly one-third of those teenagers hospitalized with covid-19 during a surge of cases early this year required intensive care, and 5 percent required mechanical ventilation.

While most covid-19 hospitalizations occur in older adults, severe disease that requires hospitalization has been shown to occur in all age groups. Covid-19 hospitalization rates among adolescents declined in January and February, the report said, but increased during March and April, even as hospitalization rates stabilized for those 65 and older, probably because of their higher rates of vaccination.

On May 10, the Food and Drug Administration authorized the Pfizer coronavirus vaccine for 12-to-15-year-olds. Here's what parents should know. (Joy Yi/The Washington Post)

Researchers suggest that the increased hospitalization among adolescents in March and April may be related to several factors, including more transmissible and potentially more dangerous virus variants; larger numbers of youths returning to school; and changes in physical distancing, mask-wearing and other prevention behaviors.

The Pfizer-BioNTech vaccine, which was authorized for those 16 and older in December, was recommended for use in 12-to-15-year-olds last month.

Even though the study is of a small group of adolescents, CDC officials and other experts expressed concern about the potential for severe disease and stressed the importance not just of vaccination but also of continued mask-wearing and other preventive behaviors until they are fully vaccinated.

“Vaccination is our way out of this pandemic,” Walensky said. “I continue to see promising signs in CDC data that we are nearing the end of this pandemic in this country; however, we all have to do our part and get vaccinated to cross the finish line.”

The new study is based on data from the CDC’s covid-19-associated surveillance network, a system of laboratory-confirmed covid-19 hospitalizations in 99 counties across 14 states, covering about 10 percent of the U.S. population.

The study looked at 376 adolescents ages 12 to 17 who were hospitalized between Jan. 1 and March 31 and tested positive for the coronavirus. Of that total, 204 youths were hospitalized primarily for covid-19, the report said, with 31 percent admitted to an intensive care unit and 5 percent requiring invasive mechanical ventilation. None of the youths died. (The report said the other 172 hospitalized youths may have been admitted for reasons not directly related to covid-19.)

About 70 percent of the 204 adolescents hospitalized primarily for covid-19 had at least one underlying medical condition — the most common being obesity. But nearly 30 percent had no reported underlying condition, the report said, “indicating that healthy adolescents are also at risk for severe covid-19-associated disease.”

Among the 204 teens, 52 percent were female, 31 percent were Latino and 36 percent were Black.

Researchers said the cumulative covid-19 hospitalization rates for the adolescents from Oct. 1, 2020, through April 24, 2021, were 2.5 to three times higher than seasonal-influenza-associated hospitalization rates during three recent flu seasons.

“Flu very rarely causes long-term symptoms and organ damage — unlike covid-19,” said Andrew Pavia, a professor of pediatrics and infectious diseases at the University of Utah. “Adolescents have many reasons to get vaccinated as soon as possible, including their own health, the ability to help control covid-19 among more vulnerable groups and the ability to return to normal life.”

Researchers said hospitalization rates may be underestimated since some clinicians may not have ordered tests for the virus, and adolescents hospitalized with the rare but serious inflammatory syndrome known as multisystem inflammatory syndrome in children might not be identified if testing took place more than 14 days after hospital admission.