When COVID-19 patients are discharged from the hospital, most are far from being well -- even if their hospital stay was fairly short.

That's among the initial findings of a study that followed Americans hospitalized for COVID-19 during the pandemic's "third wave" -- the fall of 2020 through early 2021.

Researchers found that of 253 patients discharged from the hospital, almost 85% were still not back to their previous health one month later.

In fact, more than half reported a new disability that was interfering with their daily lives, including their ability to work. A similar percentage said they had new or worsening heart and lung symptoms -- such as chronic cough, breathing problems, chest pain and an irregular, racing heartbeat.

These were not elderly, frail people, stressed Dr. Theodore "Jack" Iwashyna, one of the study's lead researchers.

Half were younger than 60, and in fairly good health before being sickened with COVID, according to Iwashyna, a professor of internal medicine at the University of Michigan in Ann Arbor.

Nor did they have especially long hospital stays: The median stay was five days, meaning half of the patients were discharged sooner.

Altogether, it highlights the lingering toll COVID-19 takes when people are sick enough to land in the hospital.

"Just because they got out of the hospital doesn't mean they're fine," Iwashyna said.

That was true in the early days of the pandemic -- and, based on this study, continued to be true in the third wave.

"COVID is still bad, even though hospital systems are prepared for it now," Iwashyna said.

Researchers are still trying to understand why COVID can evolve into a long-haul condition for some people.

"Long COVID still has no clear cause," said Dr. Thomas Gut, who heads the post-COVID recovery program at Staten Island University Hospital in New York City.

"Most recent evidence shows that the syndrome is related to inflammatory changes that occur due to the infection," said Gut, who was not involved in the new study.

Besides heart/lung symptoms, Gut said patients can have profound fatigue and neuro-cognitive changes -- commonly dubbed "brain fog." And those problems can even strike people who had milder COVID and never needed to be hospitalized, Gut said.

So while SARS-CoV-2 is a respiratory virus, the resulting disease can have broad effects in the body.

"COVID is a whole-body illness," Iwashyna said, "and so is long COVID."

The findings, published recently in the Journal of Hospital Medicine, are based on the initial patients in a larger, ongoing government-funded study. It will follow up to 1,500 patients hospitalized for COVID at large hospitals across the United States.

Iwashyna's team found that of 253 patients surveyed one month after discharge, about 55% said they had at least one new or worsening heart/lung symptom -- most commonly a chronic cough.

Meanwhile, 53% said they had physical limitations that had not been present before, including problems with daily tasks such as shopping, carrying groceries or even walking around the house.

Besides the physical toll, the study found, there was a financial one: About 20% of patients said they'd either lost or had to change their job, while 38% said a loved one had taken time off from work to care for them.

Because long COVID is complex and varied, Gut said, there is no "one size fits all" way to manage the symptoms.

One way to help hospitalized patients is through home health services after discharge.

But, Iwashyna said, few patients in this study actually received those services -- and there were hints that might have contributed to their disabilities. Of patients who reported new physical limitations, a full 77% had not received home health care.

"This makes me wonder, are we still underestimating how bad the long-term effects can be?" Iwashyna said.

Both he and Gut stressed a critical point: The best way to avert long COVID is to avoid getting COVID in the first place.

"Get vaccinated," Iwashyna advised.

The vaccines are "not perfect," he said, and breakthrough infections can sometimes occur. But they still slash the risk of getting sick, and are highly effective at keeping people out of the hospital.

A study released Tuesday by the U.S. Centers for Disease Control and Prevention found that unvaccinated people are 29 times more likely to be hospitalized for COVID than fully vaccinated people.