Pros report that an uptick in young men and women who are seriously sick with COVID-19.

With vaccination totals increasing and coronavirus cases declining across the country, many Americans are feeling a newfound sense of hope, which maybe, there is finally a light at the end of the tunnel.

But, wellbeing and government officials throughout the nation are continuing to warn that the virus is still spreading among unvaccinated populations, with a larger share of younger Americans getting infected, and in some cases, hospitalized with severe cases of this virus.

For the very first time, patients between the ages of 18 and 64 now accounts for the largest cohort of the 37,000 total patients hospitalized with the virus. With more elderly Americans vaccinated, this marks the third week that the number of hospitalized individuals in the 65 and older age group has been smaller compared to the 18-49, and also the 50-64 age groups.

Experts say the exact reason for this trend is unclear, but could include the growth of variables, relaxed attitudes towards distancing and other mitigation steps, a younger people which is not yet completely vaccinated and vaccine hesitancy. It might also be merely more younger people having the disease.

Although not all hospitalizations would be the consequence of acute illness, state officials say the trend is worrying.

“There is a really sharp increase, it seems, in younger adults… these are largely people who think that their age is shielding them from becoming very ill from COVID-19, that isn’t happening,” Cassie Sauer, CEO and president of the Washington State Hospital Association, stated during a media conference on Monday.

Dr. Chris Baliga, an infectious disease physician from the Virginia Mason Franciscan Health at Washington state, reported earlier this week he has observed more patients under the age of 40 than at any other period in the pandemic, while noting that these younger patients appear to be coming in more moderate than before.

“40 percent of those cases were below the age of 40, which is mind-boggling to me.

This tendency, according to experts, may be the result of a number of factors.

Dr. Katie Sharff, an infectious disease expert at Kaiser Permanente, told ABC News that one of the driving factors may be more young people are getting to be infected, and using this, necessarily, there’ll be more acute instances.

While earlier in the pandemic, the illness was affecting predominantly older adults, currently, coronavirus infections among Americans 18-54 accounts for the highest proportion of new cases per 100,000 inhabitants.

Sharff, too, said she’s seen more patients in her Oregon hospital between the ages of 40 and 50 requiring hospitalization, with some patients as young as 30 end up at the ICU, and a lower percentage have needed to be placed on mechanical ventilation.

Back in Oregon, daily COVID-19 cases have skyrocketed, and the number of patients hospitalized with the virus has surged by 106%.

“If you’ve got that many more young people getting infected there’ll at least be a subset who develop severe illness,” Sharff explained. Although some patients have preexisting health conditions, like obesity, what’s been”really striking with this surge” is that not all younger patients needing care have concerning medical conditions that put them at elevated risk.

Part of the problem, Sharff said, is that older people, when infected, often stay home a little longer to handle their symptoms, as opposed to elderly Americans, who normally have been hospitalized prior to their illnesses.

Since the U.S.’ vaccination plan targeted high-risk individuals by age, virtually all of these younger hospitalized patients have to be vaccinated, Samuel Scarpino, epidemiologist and assistant professor at Northeastern University, told ABC News.

“In previous surges, the vast majority of our patients were older and had chronic health conditions. We are seeing less of that very elderly population and that I think that actually speaks to the effectiveness of the vaccines,” Sharff noted.

Earlier this month, all 50 countries opened vaccinations to residents 16 years and older, but it is going to take a while for all those younger populations to be fully shielded, Scarpino clarified.

“With the 4 to 6-week delay between initial dose and the full degree of resistance, it will be a couple more weeks before those age classes have the exact same amount of protection as elderly individuals who have been vaccinated in months before,” Scarpino said.

But there are several other younger people who have chosen to not get vaccinated, Sharff said. “I believe vaccine hesitancy is fairly real,” Sharff noted.

Vaccine need has been steadily decreasing lately, as people who were excited to be inoculated get their shots and officials work to convince those wearier to be vaccinated.

According to a new ABC News/Washington Post poll, almost 1 in 4 Americans, 24 percent, are disinclined to obtain some of the coronavirus vaccinesdown from 32% three weeks ago. 16% of the polled ruled out vaccination entirely.

Additionally, more transmissible and possibly deadlier versions now accounts for the vast majority of new cases across the U.S.. The national prevalence of B.1.1.7, initially diagnosed in Britain and today, is now estimated to account for almost 60 percent of new cases, according to the CDC.

Baliga said he considers the growth of coronavirus versions, and particularly, that the B.1.1.7 variant, first identified in the uk, is supporting the rise in cases and hospitalizations among younger people.

“I feel that’s what is driving a lot of what we’re seeing in the younger people,” Baliga said, saying he viewed it as the”single most important” factor driving up amounts.

With more people are succumbing to”pandemic exhaustion,” and thus letting down their guard, with lax social distancing and COVID-19 protocols, experts say, with lots of also blaming their disease on increased social gatherings and travel.

In addition, the mix of infectious strains of this virus with reduced vaccination rates have made young people more vulnerable to this virus.