The researchers found that in the 10 months after leaving the hospital, COVID-19 patients were more than twice as likely to be hospitalized or die, compared to the general population. And even compared with people hospitalized for flu, COVID patients fared worse in certain respects.
Experts said the findings offer more evidence that recovery from severe COVID-19 can be long and difficult.
"It's a misconception to think that when most patients are discharged from the hospital they are 'back to normal,'" said Dr. MeiLan Han, chief of pulmonary and critical care medicine at the University of Michigan Health, in Ann Arbor.
For one thing, COVID-induced lung inflammation can take weeks to months to dissipate, said Han, who was not involved in the study. In some patients with severe COVID-19, she added, lung scarring can be permanent.
COVID-19 can also wreak havoc beyond the lungs. One example is blood clotting, Han said.
"I have seen patients discharged after seeming to be recovering from pneumonia only to be rehospitalized for blood clots later," she said.
Other variables are at work, too. People hospitalized for COVID-19 often have pre-existing health conditions that made them vulnerable to becoming severely ill with the infection in the first place.
Those conditions may have worsened during their COVID hospital stay, said Dr. Aaron Glatt, a spokesman for the Infectious Diseases Society of America.
One reason, he explained, is that hospitalization itself can take a toll â€” for reasons ranging from medication changes to disrupted sleep to "deconditioning." The latter refers to declines in muscle strength as well as heart and breathing capacity that can make even daily routines difficult.
Glatt is also chief of infectious diseases at Mount Sinai South Nassau in Oceanside, N.Y., where he advises patients to follow-up with their usual doctor soon after their hospital discharge. The aim is to make sure all is in order with managing their chronic conditions, including their medications.
The study â€” published online Jan. 25 in the journal PLOS Medicine â€” analyzed medical records from nearly 25,000 U.K. adults who survived a COVID hospitalization in 2020. The majority (about 62%) were age 60 or older.
Each patient was compared with five people from the general population of the same age, sex and area of residence. They were also compared with more than 16,000 people hospitalized for the flu between 2017 and 2019.
Overall, COVID-19 patients fared worse than the general population: By the six-month mark, almost 35% had been hospitalized again or died, compared to 15% of the comparison group.
COVID-19 patients were often on par with flu patients when it came to the risk of being rehospitalized for various causes. However, their odds of dying from any cause were higher: 7.5% had died six months after discharge, compared to 5% of influenza patients.
Meanwhile, COVID-19 patients with pre-existing dementia had a higher risk of being hospitalized or dying from that disease, compared with influenza patients. And as a group, COVID patients were 37% more likely than flu patients to be hospitalized for a mental health condition or problems with memory or thinking skills (cognition).
"The increase in cognitive-related readmissions is clearly concerning," Han said. "While we know many patients have complained of 'brain fog' after recovering from COVID-19, how the infection may be impacting the brain or cognitive function, and for how long, remains an active area of research."
COVID-19 patients in the study were all hospitalized in 2020. So it's not clear whether the same numbers would be seen today, according to lead researcher Krishnan Bhaskaran, a professor at the London School of Hygiene and Tropical Medicine.
"Since the patients in our study were hospitalized, we have certainly seen changes in care, new (COVID) variants, and a major rollout of vaccines," Bhaskaran said.
But the experts agreed that the bottom line for hospitalized patients remains the same: After discharge, keep all follow-up appointments with your doctors, and let them know if any symptoms worsen or new ones arise.
"For everyone else," Bhaskaran said, "my main advice would be to get vaccinated or boosted when the opportunity arises, as this is the best way of avoiding a COVID hospitalization in the first place."
Harvard Medical School has a COVID resource hub.PLOS Medicine