(NEW YORK) — The COVID-19 pandemic is not over yet and hospitals are seeing a startling uptick in younger patients filling hospitals.

States including Florida, Washington, Michigan, Colorado and Pennsylvania are reeling from a rise in virus cases and hospitalizations among younger people.

Experts say group activities, vaccine hesitancy, virus variants, return to work and pandemic fatigue are to blame.

Dr. Rupali Limaye, an associate scientist in International Health at the Johns Hopkins Bloomberg School of Public Health, told ABC News that younger people — last to get the vaccine — are more susceptible to getting sick, especially with more contagious variants.

“There has been a huge shift with a lot of folks going back to work. Individuals that are older aren’t going to work … whereas you have people between ages 18 to 49 and a lot of them have started … back in person, increasing their risk of exposure,” Limaye said. “You couple all of that together with the variants that are more infectious and severe, I think that’s the reason why you’re seeing more young people coming into hospitals.”

Some people feel a false sense of security when the people around them are vaccinated, even if they, themselves, are not, Limaye also said.

“I think people infer that, if all these other people are getting it, that it’s not so important for me to hurry up and get it, especially if it’s a pain to get it. I think there is a little bit of risk compensation taking place there,” Limaye said.

In Florida, infections have climbed over the last few months, particularly among young people.

Gov. Ron DeSantis allowed anyone 18 and older to get a shot on April 5. So far 16% of the state’s population between 16 to 44 are fully vaccinated, according to Florida’s latest COVID-19 report published Tuesday. Overall, more than 8.6 million people in Florida have either received their first COVID-19 vaccine dose or completed the series.

In Fort Lauderdale, Florida, the chief medical officer of Broward Health Medical Center reported a “slow wave” of young patients being admitted into hospitals.

Broward County, where the hospital is located, also has the most confirmed variant cases in the nation with the U.K., Brazilian and California variants, according to Centers for Disease Control and Prevention data.

“Usually between the age of 25 and 44 is the age that we are seeing, and when you compare that to the statistics of the increases in incidents in the community, that’s the age that is most susceptible,” Joshua Lenchus, Broward Health Medical Center’s chief medical officer, said to local ABC affiliate WPLG.

Florida reported 2,776 new virus cases among patients aged 15 to 44 Monday, which comprised 53% of all new cases reported, according to state data. That age group accounts for 15% of the state’s hospitalizations.

Lenchus said the age group entering hospitals “is a little more hesitant, I think, to get the vaccine than people who are older.”

More than 600 hospitalizations have been reported from Washington state’s 44 hospitals — the most the state has seen in months.

Dr. Josh Griggs, the chief quality officer at Skagit Regional health says restlessness from a year of lockdown is, in part, driving the numbers.

“The younger population has pandemic fatigue. They’re not wearing their mask or social distancing,” he said to Fox affiliate KCPQ.

Experts said the contagious B117 variant, which first emerged in the U.K., is also driving the surge and impacting young people.

COVID-19 fatigue and group gatherings have also been blamed for surges among younger people in Michigan.

In early April, Michigan officials said their surge was due to “variants, outbreaks among schools/sporting teams and a high case rate among 10- to 19-year-olds and now increasing rates among all age groups through 59, and COVID-fatigue,” during a call with local media.

In Michigan,10- to 19-year-olds are testing positive for COVID-19 at a higher rate than any other age group, according to an April 20 report, followed by patients ages 20 to 49.

An average of nine people a day aged 18 and under were admitted to the hospital with COVID-19 in the week that ended April 17– up 183% from Feb. 28.

That report also found that the number of active outbreaks was up 10% from the week prior with 312 school outbreaks as well as several clusters related to K-12 sports.

On April 9, Gov. Gretchen Whitmer urged Michiganders to voluntarily suspend in-person activities for high schools, indoor drinking and youth sports for two weeks.

Colorado is also seeing a rapid increase in COVID-19 cases among children, with a jump among middle school- and high school-aged children, state epidemiologist Dr. Rachel Herlihy said Tuesday.

She said cases among children 11 to 17 spiked dramatically, but did not explain why. Gov. Jared Polis stressed that schools are safe and said the surge in COVID-19 cases among school-aged children could be related to outings with family members.

CDC director Dr. Rochelle Waleknsky said during a April 5 briefing: “Cases are increasing nationally, and we are seeing this occur predominately in younger adults,” citing the increasing spread of variants, youth sports and extracurricular activities as reasons.

Misinformation about the vaccine is only adding fuel to the fire.

“[What] breaks my heart is that a lot of people don’t know who they can go to that they can trust because they are bombarded by all this misinformation. You still having a large proportion of the population under the age of 55 that has not gotten the vaccine here in the U.S. And so until that happens, I think we’re still gonna see more younger people presenting these cases at hospitals,” Limaye said.

While it’s too soon to predict if young people could drive a fourth wave, Limaye said getting the shot is more dire than ever.

“Get a shot. If you can’t get a shot [or] you have questions about the shot, find someone to speak with to make an evidence-based decision,” she said.

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