New Hypothesis on Long COVID Cause

Long COVID may be caused by “reservoirs” of SARS-CoV-2 that lie dormant in the body. That’s according to new research at the University of Colorado School of Medicine.

Long COVID is defined as symptoms of COVID that persist for more than four weeks. These may include cough, shortness of breath, fatigue and brain fog. Some research has suggested up to one out of every four people who become ill with COVID will get long COVID.

Colorado Associate Professor of Immunology, Brent Palmer, hypothesised that viral “reservoirs” cause the immune system to be overactive in long COVID patients.

So Palmer took blood samples from 20 healthy people and 20 with long COVID. Their blood was incubated with small pieces of the virus. 

His lab found that in patients with long COVID, the immune-response was far higher. There were 100 times more T-cells produced in the long COVID patients’ blood than in those of healthy individuals.

Even six months after infection, long COVID patients still have an average of 50% of their immune system geared towards countering the coronavirus. Prof Palmer, formerly an AIDS researcher, points out that that is higher even that people infected with HIV.

Moreover, there was a specific connection between T-cell activity and pulmonary function. 

“The higher the frequency of COVID-specific T cells in the blood of that individual, the worse their pulmonary function tests were,” said Palmer. “That showed a really strong connection between these T-cells that were potentially driving disease and an actual readout of disease, which was reduced pulmonary function. That was a critical discovery.” 

Long COVID has been liked to post-viral fatigue and chronic fatigue syndrome, whose causes are not clearly understood. This research links long COVID characteristics more directly to the coronavirus itself.

“We think it’s an overexaggerated immune response that’s causing the problem,” he says. “What we hypothesise is that there’s residual virus somewhere in the body, but it’s not detected by a nasal swab.” 

The findings help explain why long COVID may be attenuated by booster doses of the vaccine. By raising the immune response further, these individuals may be able to finally eliminate the virus completely from their body. 

With the same goal in mind, anti-COVID retroviral drugs like Paxlovid may also be effective for long COVID.

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