In recent years, doctors and scientists have paid more attention to illnesses that last a long time after someone recovers from an infection.
Two of the most well-known examples are long COVID and a condition called ME/CFS, which stands for myalgic encephalomyelitis/chronic fatigue syndrome.
Experts believe that about 400 million people around the world could have long COVID, and nearly half of them also meet the criteria for ME/CFS. These two illnesses were often misunderstood or ignored in the past, but that is starting to change.
Now, researchers are studying them as part of a bigger group of diseases known as post-acute infection syndromes, or PAISs for short.
A new review by Dr. Anthony Komaroff from Mass General Brigham and Dr. Robert Dantzer from MD Anderson Cancer Center brings together years of research. Their work was published in two major science journals, and it helps explain what might cause these illnesses and how we might treat them in the future.
The researchers found that people with long COVID and ME/CFS share many of the same biological problems. These include inflammation in the brain, trouble making energy in cells, and problems with the immune system.
They also suggest that certain parts of the brain, which normally help us when we are sick, may stay “switched on” even after the infection is gone. This may be the reason people continue to feel tired and unwell for a long time.
Dr. Komaroff first became interested in ME/CFS over 40 years ago, when he met patients who didn’t recover after a common viral illness.
At the time, regular medical tests couldn’t find anything wrong, so some people believed the symptoms were just in the patients’ heads. But over the years, researchers discovered that people with ME/CFS have real biological changes in many parts of their bodies.
In their recent reviews, the researchers looked closely at what causes the symptoms and why they can last for years. They found several important biological issues, including brain inflammation, reduced energy production, immune system problems, changes in blood vessels, an unhealthy gut microbiome, and cellular stress.
One interesting idea they discuss is called “sickness behavior.” This is a natural response the body has when it fights off an infection—feeling tired, avoiding activity, and resting. It helps save energy for the immune system.
But in people with ME/CFS or long COVID, this response may not turn off, even after the infection is gone. That could explain why symptoms like fatigue and brain fog last so long.
They also found that many of these biological problems can make each other worse, creating a cycle that keeps the illness going.
The COVID-19 pandemic has helped change how people see ME/CFS. Long COVID has shown that a viral infection can lead to long-term illness, which supports what many ME/CFS patients have said for years. It also shows that similar problems can happen after other infections like Lyme disease or West Nile virus.
The reviews found that both ME/CFS and long COVID show similar brain scans, nervous system problems, immune system issues, and trouble with energy and heart function. These similarities suggest the illnesses have the same root causes.
Right now, there are no approved treatments for either illness, but vaccines and early treatment of COVID-19 can help lower the risk of long COVID. The researchers think that calming brain inflammation might be key to future treatments. Several new therapies are being tested, but they are still in early stages.
Looking ahead, two big research questions remain. First, do other post-infection illnesses show the same biological patterns as ME/CFS and long COVID? Second, which new treatments can reduce brain inflammation in humans?
Finally, doctors and scientists want to raise more awareness about post-acute infection syndromes. Many people, even in healthcare, still don’t know much about these conditions. Understanding and accepting them can help improve diagnosis, research, and treatment.
If you care about COVID, please read studies about vitamin D deficiency linked to severe COVID-19, death, and how diets could help manage post-COVID syndrome.
For more health information, please see recent studies about COVID infection and vaccination linked to heart disease, and results showing extracts from two wild plants can inhibit COVID-19 virus.
The study was published in Cell Reports Medicine.
Copyright © 2025 Knowridge Science Report. All rights reserved.
