Between 7 million and 23 million Americans are estimated to have long COVID, according to a recent report by the U.S. Government Accountability Office.
With more than 200 symptoms identified so far, ranging from a lingering cough, fatigue, peeling skin, hallucinations, and a sensation some patients describe as “brain on fire,” they can’t all have the same thing, right?
Experts are starting to ask that question, too.
As researchers race to understand just what long COVID is, an increasing number are attempting to divide the new, potentially debilitating disease into groups.
Dr. Alexandra Brugler Yonts, an infectious disease specialist at Children’s National Hospital in Washington, D.C., and the head of its new Pediatric Post-COVID Program, told Fortune she divides the types of long COVID into five categories, grouped by causes.
1. Long-term direct effects
COVID damaged the organs of these patients during the course of disease, causing long-term health repercussions. A recent study published in the journal Radiology found that roughly half of the nearly 100 COVID patients examined had persistent lung damage a year after infection.
During infection, the virus triggered the body’s release of inflammasomes, which kill infected cells. But the fallout can wreak havoc in various organ systems, especially if the process persists after infection.
In dysautonomia, patients experienced direct damage to the autonomic nervous system that persists after infection. One type of dysautonomia thought to afflict long-COVID sufferers is postural orthostatic tachycardia syndrome, or POTS. Potentially autoimmune in nature, the syndrome causes disruptions in heart rate and blood pressure in response to changes in position.
4. Ongoing viral activity
In these patients, COVID isn’t quite ready to give up yet. Ongoing viral activity could be caused by “ghost” virus cells that can linger for months after initial infection. Recent research has found that such cells, when located in the gut, can cause ongoing gastrointestinal symptoms, like diarrhea, that aren’t typical of a respiratory virus.
5. Altered immune response
This can be seen alone or in combination with the other categories, Yonts said. In order to bring itself back to normal during COVID infection, the immune system overcorrects, resulting in extended susceptibility to a number of viruses the body might usually fight off. Anecdotally, she’s heard of patients in their twenties who had COVID and then came down with a slew of other illnesses in short order, like mono and strep.
Know thine enemy
When it comes to COVID long haulers, there are clearly “different pathologies at play,” Yonts said. “I don’t think there’s one process that is ‘long COVID’ in every single person. There are multiple processes going on.”
The sooner researchers can nail down the causes, the sooner they can develop targeted treatments, she said. Currently, symptoms are treated, and patients many undergo therapies to regain lost abilities—but not much more can be done.
“Once we can more solidly tease that out, it will lead to better ways to manage those patients and more focused pharmaceutical treatments,” Yonts said.