“I think that it’s a much more complex picture than just inflammation, or just autoimmunity, or just immune dysregulation. And it’s probably a combination of all three causing a cascade of effects that then manifests itself as brain fog, or shortness of breath, or chronic fatigue,” says Alexander Truong, MD, a pulmonologist and assistant professor at Emory University, Atlanta, who also runs a long-COVID clinic.
Long COVID, post–COVID-19 condition, and postacute sequelae of SARS-CoV-2 (PASC) are among the terms used by theto describe the long-term health issues faced by an estimated 10%-30% of people infected with COVID-19. Symptoms – – can range from inconvenient to crippling, damage multiple organ systems, come and go, and relapse. Long COVID increases the risk of worsening existing health problems and , including cardiovascular disease and .
So far, research suggests there is no single cause, condition, or disease that explains why some people have an extensive range of symptoms long after the early COVID-19 infection has cleared up. Many experts believe some combination of biological processes – including the virus hanging around in our bodies, inflammation, autoimmunity, tiny blood clots, immune system problems, and even thesuch as the – could be the culprit, a theory also supported by a comprehensive and in-depth review of long-COVID studies in the journal Nature Reviews Microbiology.
“It’s become clear over the last couple of years that there are different [symptoms] of long COVID … that cannot all be lumped together,” says Michael Peluso, MD, an assistant professor of medicine and an infectious diseases doctor at the University of California, San Francisco.
Inflammation and a virus that hangs around
Multiple studies have shown that the virus or pieces of it can remain in many parts of the body, including the kidneys, brain, heart, and gastrointestinal system, long after the early infection.
“One major question that I think is the area of most intense investigation now is whether there is viral persistence that is driving immune dysregulation and therefore symptoms,” says Dr. Peluso.
A smallstudy, for example, found evidence that reservoirs of the coronavirus could linger in patients up to a year after they’re first diagnosed.
An earlierfound that patients with post-COVID-19 symptoms had higher levels of three cytokines – small proteins that tell the body’s immune system what to do and are involved in the growth and activity of immune system cells and blood cells. Researchers said the results supported the theory that there is persistent reprogramming of certain immune cells, and that the uncontrolled “self-fueled hyperinflammation” during the early COVID-19 infection can become continued immune cell disruption that drives long-COVID symptoms.
“Long COVID is more likely due to either an inflammatory response by the body or reservoirs of virus that the body is still trying to clear … and the symptoms we’re seeing are a side effect of that,” says Rainu Kaushal, MD, senior associate dean for clinical research at Weill Cornell Medicine in New York.
that immune system recovery appeared different, compared with those who were infected with other common coronaviruses.
These findings also support concerns that some experts express over the long-term risks of COVID-19 infections in general, but especially repeat infections.
“Anything that kind of revs up inflammation in the body can boil that pot over and make the symptoms worse. That’s very easily an infection or some other insult to the body. So that’s the generalized hypothesis as to why insults to the body may worsen the symptoms,” says Dr. Truong.