COVID-19 fragments may cause problems after infection: Report

Fragments of COVID-19 left behind after your body's immune system has fought off all signs of infection may continue to trigger immune responses, researchers said in a National Institutes of Health (NIH) report published on Feb. 27. 

While most COVID-19 cases are mild, these ongoing immune responses could lead to life-threatening complications. 

Researchers said these fragments, when left behind, can trigger overactive immune responses, causing dangerous inflammation. 

Researchers said that inflammation can impact many different areas of the body, even uninfected ones, resulting in common long COVID effects. 

"It’s not clear why SARS-CoV-2 can cause such inflammation while other coronaviruses responsible for common colds don’t," the NIH report read. 

What is long COVID? 

Long COVID refers to a "range of health problems that emerge, persist, or recur following acute COVID-19 illness," according to the Centers for Disease Control and Prevention. 

Scientists don’t yet know what causes long COVID, but it encompasses about 200 different symptoms. Among the more common symptoms are chronic pain, brain fog, shortness of breath, chest pain and intense fatigue, according to Yale Medicine. 

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"People with long COVID can have a wide range of symptoms that can last weeks, months, or even years after infection," the CDC said. "Sometimes the symptoms can even go away and come back again. For some people … long COVID can sometimes result in disability. Long COVID may not affect everyone the same way."

How the COVID-19 hacks the immune system

According to the NIH, the immune system fights viruses by breaking down viral proteins into smaller fragments called peptides. 

Researchers said that those fragments should be used to train the immune system to remember the virus in the future to protect the body if it gets infected again. 

But when it comes to COVID-19, doctors said it's more complicated than that. 

"The textbooks tell us that after the virus is destroyed, the sick host ‘wins,’ and different pieces of virus can be used to train the immune system for future recognition. COVID-19 reminds us that it’s not this simple," NIH research lead Dr. Gerard Wong explained. "For comparison, if one were to assume that after food gets digested into its molecular components, then its effects on the body are over, it would be very liberating. I wouldn’t have to worry about the half-dozen jelly donuts I just ate. However, this simple picture is not correct."

The NIH said these findings could help doctors better determine how COVID-19 will impact a particular patient and whether or not it will be a mild case or cause further inflammatory issues.