Children and teens who’ve had COVID are at greater risk for blood clots, heart problems, kidney failure, and Type 1 diabetes, according to a new report released Thursday by U.S. health officials.

Researchers with the U.S. Centers for Disease Control and Prevention examined the electronic health records of nearly 800,000 U.S. children ages 0 through 17 who had COVID from 2020 through 2022, and compared them with that of nearly 2.5 million children who had not been diagnosed with COVID during the same time period.

They found that young people who had been diagnosed with COVID were about two times more likely to experience a blood clot in the lung—and nearly two times more likely to experience myocarditis, inflammation of the heart muscle; cardiomyopathy, a disease that makes it more difficult for the heart to function correctly; or blood clots in veins—in the year following their illness.

They were also roughly 1.3 times as likely to experience kidney failure, as well as Type 1 diabetes, an autoimmune disorder that destroys the pancreas’s ability to make insulin, according to the study.

Post-COVID conditions—defined as new or recurring health problems that occur four or more weeks after COVID infection, also known as “long COVID”—are poorly understood. Myriad efforts are underway to elucidate the condition—or multiple conditions. But such studies focus predominantly on adults, not children, according to the CDC.

COVID prevention strategies, including vaccination, are critical for preventing COVID, post-COVID conditions, and COVID-related diseases like MIS-C, or multisystem inflammatory syndrome in children. MIS-C patients fully recover from COVID, if they even had symptoms, and are fine for four to 12 weeks before developing a rare, inflammatory-based illness that can be fatal.

Up to one in five American adults who’ve had COVID-19 are living with long COVID, U.S. officials have recently stated. And an estimated 1 million Americans have been forced to leave the labor force because of medical complications from the nascent condition.

An estimated 5% to 10% of children who’ve had COVID go on to develop long COVID, Dr. Alexandra Brugler Yonts, an infectious disease specialist at Children’s National Hospital in Washington, D.C., told Fortune in May.

“People are like, ‘Oh, it’s only 5%,’ but we talk about death being 1% and it’s still a big deal,” she said.

At the lower end of that range are kids with “true long COVID, whatever that means,” she added. “We’re still figuring it out.”