New data from the Centers for Disease Control and Prevention shows young adults ages 20 to 44 face a substantial risk of serious illness and hospitalization from the coronavirus. While early reports from China showed the majority of deaths occurred in patients age 60 or older or those with underlying health issues, that doesn't mean younger people are immune from severe illness.

The CDC said there were a total of 4,226 cases confirmed in the U.S. as of March 16, and it analyzed the data on 2,449 of those cases where ages for the patients were known. Of those:

6% were people age 85 or older

25% were 65-84 years old

18% were 55-64 years old

18% were 45-54 years old

29% were ages 20-44 years old.

Only 5% of cases occurred in children and teens age 19 or under.

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The CDC said as of March 16, there were 508 patients known to have been hospitalized in the U.S. — 12% of the total cases. Twenty percent of those hospitalized were between the ages 20 and 44 — so younger adults accounted for a large portion of the hospitalizations.

In fact, people in the 20 to 44 age range accounted for more hospitalizations than people 85 or over (9%), 55 to 64 years old (17%) and 45 to 54 years old (18%).

The largest age group who were hospitalized were between 65 and 84 years old; they accounted for 26% of hospitalizations.

As of Thursday, the number of confirmed cases in the U.S. has swelled to over 9,000, according to data compiled by Johns Hopkins, so the figures on age breakdowns could be different.

While officials have repeatedly warned that older people are the most vulnerable, they are now making sure younger people know they can also face serious risks. White House coronavirus response coordinator Dr. Deborah Birx says a similar trend has been seen of young people being hospitalized in Europe.

"There are concerning reports coming out of France and Italy about some young people getting seriously ill, and very seriously ill in the ICUs," Birx said in a White House news conference Wednesday.

"We think part of this may be that people heeded the early data coming out of China and coming out of South Korea about the elderly or those with preexisting medical condition who are at particular risk. It may have been that the millennial generation ... there may be disproportional infections among that group," Birx continued.

She again urged millennials to practice social distancing. "We need them to be healthy," she said.

On "CBS This Morning," Dr. Tara Narula said the new CDC numbers are very important. Not only are 20% of the hospitalized patients aged 20 to 44, 12% of those in ICU are in that age group as well.

"We're still learning a lot about this virus," Dr. Narula said. "So for those young individuals who think 'It can't happen to me, I'm not susceptible to this' — that's just not the case."

To be clear and avoid confusion - 20% of the patients requiring hospitalization were in the ages 20-44. 12 % of the patients requiring ICU level care were ages 20-44 https://t.co/G8oYmPONfE — Tara Narula M.D. (@drtaranarula) March 19, 2020

While officials have been urging everyone to practice social distancing, some young people haven't been heeding the warning. Many packed into bars last weekend before cities and states began shutting them down, and spring-breakers still flocked to crowded Florida beaches, showing little concern.

"If I get corona, I get corona. At the end of the day, I'm not going to let it stop me from partying," Brady Sluder told Reuters as he enjoyed spring break in Miami. "This virus ain't that serious," said 21-year-old Atlantis Walker.

But health experts say that's a dangerous misconception.

"This big idea of social distancing, we can't hammer it home enough," Dr. Narula said. "This comes down to something we call the reproduction factor — that's how infectious I am. So if I [hypothetically] have the disease, I can spread it, we think with coronavirus, to three people. That reproduction number is affected by the virus properties itself, who is susceptible, but also the duration of contact with individuals and the number of people you contact."

Decreasing the number of people you contact and the duration can significantly slow down the spread of the virus, she said.

During a press conference Thursday morning, New York Governor Andrew Cuomo, joined by his 22-year-old daughter Michaela, urged young people to stop partying and practice social distancing.

Cuomo, sitting by his daughter Michaela, warns young people to not be "unintelligent and reckless" by continuing to party during the coronavirus crisis. He shares a quote from his grandfather: "We grow too soon old and too late smart" https://t.co/ACLdYl0RqA pic.twitter.com/0NMftaVLYl — CBS News (@CBSNews) March 19, 2020

He then quoted his grandfather: "When I was youngish —16, 17, 18 — and I would do something that he didn't like, he'd look at me and say, 'We grow too soon old and too late smart,'" Cuomo said.

"These pictures of young people on beaches, these people saying 'This is my spring break, I'm out to party. It's my time to party.' This is so unintelligent and reckless, I can't even express it," he added.

Cuomo joked that while he can order a quarantine of a state, he can't tell his daughter anything. He urged his daughters and all other young people to weigh the risks of going out during this time.