While older people remain the most vulnerable to succumbing to complications from the novel coronavirus, younger patients — including those with no preexisting conditions — can also become seriously ill with the disease and even be killed by it.

At least 759 people under the age of 50 have died in the U.S. from the virus that causes COVID-19, The Washington Post reported Wednesday. At least 45 of those deaths were among people in their 20s and at least 190 among people in their 30s, the paper said.

Even patients under the age of 20 have not been spared. The Post said at least 9 people in the U.S. who were 20 or younger have died because of the illness.

The paper noted that the actual number of deaths among young people is likely higher as some states don’t provide data about coronavirus deaths based on age group.

Health experts have repeatedly warned younger Americans to take the coronavirus pandemic seriously. “Even though you are young, you are not absolutely invulnerable,” Dr. Anthony Fauci, the top U.S. infectious disease expert, said last month.

An earlier analysis by the Centers for Disease Control and Prevention found that younger Americans were making up a sizeable bulk of known coronavirus hospitalizations. Adults aged 20 to 54 accounted for 38% of those who required hospital treatment, the agency said in March. Among 121 patients known to have been admitted to the intensive care unit, 48% were under the age of 65, the CDC added.

As the Post noted this week, many young people hospitalized because of COVID-19 had preexisting conditions like hypertension and asthma. But some younger patients have suffered severe outcomes even without a history of health problems.

“I think everyone should be paying attention to this,” Stephen Morse, a professor of epidemiology at Columbia University, told The New York Times after the CDC published its analysis in March. “It’s not just going to be the elderly. There will be people age 20 and up. They do have to be careful, even if they think that they’re young and healthy.”