Nearly three years into the pandemic, scientists are still trying to figure out why some people get very long COVID. COVID has affected millions of people around the world, yet only a small proportion of affected people have long-lasting symptoms, including fatigue, lung problems, brain fog, and other neurological symptoms. As a result, experts looked at various studies conducted across the globe and stated that fall cells and mono virus might be playing a role in cases of long-term COVID.

Several studies have shown that the coronavirus can infect fat cells. These studies have shown viruses can reproduce in fat tissue. Hence, it raises the possibility of using the fat tissue as a "reservoir" for the lasting symptoms of long-term COVID. Dr. Sabra Klein, a Johns Hopkins professor who specializes in immunity, stated that this finding supports the hypothesis that women are at increased risk of COVID infection as they tend to have more fat tissue in comparison to men.

On the other hand, several experts have suggested that the Epstein-Barr virus can also be associated with COVID. Dr. Timothy Henrich, a virus expert at the University of California, San Francisco, revealed that his team has found immune markers signaling Epstein-Barr reactivation in the blood of long-term COVID patients. He explained that the inflammatory response to a COVID infection activates herpes viruses, which can remain in the body after causing an acute infection. He added that the reactivation can cause mononucleosis or produce symptoms such as fatigue and a cold. 

(Source: https://www.hindustantimes.com/lifestyle/health/long-covid-could-mono-virus-or-fat-cells-be-playing-roles-101672153843799.html )