Most COVID-19 cases resolve relatively quickly. But some patients go on to develop long COVID, a constellation of debilitating chronic health issues that can persist for weeks, months or even years.
Scientists around the world have been struggling to get a better handle on precisely what it means and how it evolves.
New British research finds that as many as 6 in 10 long COVID patients continue to battle some form of mild organ impairment -- sometimes involving more than one organ -- a year after their initial COVID-19 diagnosis, giving rise to some combination of breathing difficulty, mental impairment and a lower quality of life.
Most of these patients were never hospitalized with serious COVID-19 symptoms to begin with.
"We know that the people who have been hospitalized with COVID at the beginning are more at risk of developing new chronic diseases, such as diabetes, and higher rates of heart disease," said study author Amitava Banerjee, a professor of clinical data science at the Institute of Health Informatics at University College London.
"But what's important about our study is that it mainly involves patients who were never hospitalized with COVID. Their initial illness was never severe enough," he said.
Even though just 13% of the 536 patients enrolled in the study had been hospitalized due to their initial COVID-19 infection, they all had long COVID symptoms, Banerjee noted.
At an average six months after their initial COVID-19 diagnosis, 38% of the study patients had extreme breathlessness; 48% had trouble thinking clearly, and 57% reported poor health-related quality of life.
For the study, participants each had a multi-organ MRI body scan roughly at the six-month mark after their initial COVID-19 diagnosis.
About three-quarters of the patients were women, and 9 in 10 were white. About a third were British healthcare workers. Most were infected during the pandemic's first wave in 2020, before COVID-19 vaccines were available.
The scans revealed that 62% had some form of mild organ impairment, variously involving the heart, liver, kidney and/or spleen.
Those patients had a second MRI scan at one year. By that point, their symptoms had resolved somewhat, though 30% still had breathing problems; 38% continued to have thinking and memory issues, and 45% reported a diminished quality of life.
About 59% still had single organ impairment, and 27% had multi-organ impairment after a year.
"In most cases, if not the vast majority, what we found was mild organ impairment," Banerjee said, adding that data from several countries make it clear that some people do get better.
He also emphasized that this study doesn't prove that long COVID causes organ trouble, only that there is an association between the two.
Because "organ damage" suggests clear cause and effect in a scientific context, Banerjee referred to the trouble as "organ impairment."
Still, he emphasized that the scans clearly indicate that the organs of these long COVID patients were "not normal" and "not functioning properly."
"When patients say they have persistent symptoms after COVID, we need to do service to these people, and assess them properly across multiple organs," Banerjee said.
At the same time, he said much about long COVID remains unclear.
"Basically, when it comes to figuring this all out we're building the plane while we're flying it," Banerjee said. "There's still a lot we don't understand, and we're still going to need to do a lot more research."
Dr. Davey Smith is head of infectious diseases and global public health at the University of California, San Diego's Department of Medicine.
He agreed with Banerjee that "we remain very much in the dark about long COVID," especially the exact biological mechanisms that cause it.
"It is likely different for different people, making it even harder to figure out all the reasons why someone gets long COVID," Smith said. "Many researchers, including myself, are trying to figure this out, but I think this is going to require much more research."
Unfortunately, Smith said, neither COVID-19 nor long COVID is likely to disappear anytime soon.
"As an infectious disease doctor, I will be taking care of COVID patients for the rest of my career," he said. "I also think long COVID will be around for the rest of my career."
At the same time, Smith also pointed to two pieces of good news. One, he said, is that "some people with long COVID do eventually resolve." The other is that the COVID-19 vaccine effectively reduces the risk for developing long COVID in the first place.
The findings were published recently in the Journal of the Royal Society of Medicine.
The U.S. Centers for Disease Control and Prevention has more on long COVID.
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