In March and April, when COVID-19 vaccinations were starting to keep older adults out of the hospital, more and more children between 12 and 17 years old were being admitted. Many were seriously sick: around one-third of kids in this age group who were in the hospital for COVID-19 this year were in the intensive care unit, a new Centers for Disease Control and Prevention report shows. None died.

The risk of getting seriously ill and needing to be hospitalized from COVID-19 increases with age, but kids and teenagers can still get sick. Hospitalization rates from COVID-19 in this group were, overall, around 2.5 to 3 times higher than those from the flu over the last three flu seasons. The new CDC data underscores the importance of COVID-19 vaccination for adolescents, CDC Director Rochelle Walensky said during a press briefing Thursday. Vaccine shots are now authorized for anyone over the age of 12.

“[The findings] force us to redouble our motivation to get our adolescents and young adults vaccinated,” she said.

The CDC report looked at data from a network of health centers in 14 states. It found that 204 adolescents were hospitalized for COVID-19 between January 1st and March 31st, 2021. Of that group, 64 were admitted to an intensive care unit and 10 were placed on a ventilator. Around two-thirds had underlying medical conditions, but about 30 percent did not, showing that healthy kids can still get seriously sick.

Centers for Disease Control and Prevention

Hospitalization rates for this age group peaked during January, dropped off in February, and then started climbing back up during the beginning of March. Maryland and Michigan both had their highest ever rates in April — both states saw overall surges in case numbers during that time.

A combination of factors may have contributed to that uptick, the CDC report said. Kids started returning to school and in-person extracurricular activities during that time, and COVID-19 outbreaks can occur in those environments. In addition, variant forms of the virus that can spread more easily were circulating. Some areas also started to ease up on COVID-19 restrictions as adults got vaccinated against the disease, which could have let the virus spread among people, including adolescents, who weren’t yet eligible for the shots.

Almost 6.4 million kids between 12 and 17 in the US have had at least one dose of a COVID-19 vaccine, as of June 4th.