A new Centers for Disease Control and Prevention study found recent increases in COVID-19 hospitalizations among adolescents that the agency’s director calls “troubling.”

The study, released Friday, found that COVID-19 hospitalizations in 12- to 17-year-olds peaked in January at 2.1 cases per 100,000 people, fell to 0.6 by mid-March and then rose again to 1.3 in April. 

Nearly one-third (31.4%) of adolescents who were hospitalized were admitted to an intensive care unit, and 5% required invasive mechanical ventilation, the study said. There were no associated deaths.

The data, collected from a coronavirus surveillance network covering 99 counties in 14 states, are further proof that COVID-19 prevention measures — including vaccinations, mask wearing and social distancing — should continue to be followed, the CDC said.

In a statement released Friday, CDC Director Dr. Rochelle Walensky said that she is "deeply concerned by the numbers of hospitalized adolescents and saddened to see the number of adolescents who required treatment in intensive care units or mechanical ventilation."

"Much of this suffering can be prevented," she added, noting that adolescents should wear masks and take precautions to protect themselves and others from COVID-19.

"I ask parents, relatives and close friends to join me and talk with teens about the importance of these prevention strategies and to encourage them to get vaccinated," she concluded. "If parents or their teenagers have questions or concerns, I suggest they talk with their adolescent’s healthcare provider, local health department or neighborhood pharmacist."

The study analyzed data from up until April 24. On May 12, the CDC’s advisory board recommended that emergency authorization for the Pfizer-BioNTech vaccine be extended to 12- to 15-year-olds, making it the first vaccine available to that group. Prior to then, the Pfizer vaccine was approved for individuals 16 and older, while the Moderna and Johnson & Johnson shots are only available to people 18 and older.

About a quarter of Americans ages 12 to 17 have received at least one vaccine dose, but only about 9% are fully vaccinated.

“In the month leading up to the recommendations of the Pfizer COVID-19 vaccine for teens and adolescents 12 and older, CDC observed troubling data regarding the hospitalizations of adolescents with COVID-19,” CDC Director Walensky told reporters Thursday. “More concerning were the number of adolescents admitted to the hospital who required treatment in the intensive care unit with mechanical ventilation.”

The COVID-19 hospitalization rate of 12- to 17-year-olds was lower than for adults but higher than for children 5 to 11.

The researchers said the increased hospitalization rates in adolescents might be related to more highly transmissible variants, larger numbers of children returning to schools or other in-person indoor activities, and changes in behavior, including mask wearing and social distancing. 

The study noted that COVID-19 transmission occurs more easily in high schools than in elementary schools and that outbreaks have been attributed to high school extracurricular activities.

“Until teens are fully vaccinated, they should continue to wear masks and take precautions when around others who are not vaccinated, to protect themselves, their friends, family and community,” Walensky said.

The study also said that the hospitalization rates for the 12-17 age group was 2.5 to three times higher than for flu cases in recent years.