Why is ME/CFS research key to understanding long COVID?

A large number of people with long COVID are reporting similar symptoms to those who have myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). Scientists are now researching the similarities between the two conditions. Many hope that exploring this interconnection will result in a better understanding of both long COVID and ME/CFS.

What is the connection between long COVID and ME/CFS?

With 1.2 million people currently thought to have long COVID symptoms in the UK, the condition is now considered to be "a huge problem and major crisis". However, as a condition of the COVID-19 pandemic that was only recognised just over a year ago, long COVID is still poorly understood. The National Institute of Health Research (NIHR) has expressed the "urgent need to research treatments and management for people with long COVID".


Researching a new condition is a daunting and lengthy task, but a significant possible 'overlap' between long COVID and myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a cause for hope. In fact, as many as 50% of people with long COVID are qualifying for an ME/CFS diagnosis because their core symptoms are the same. 

ME/CFS is not a newly recognised condition and affects millions worldwide. Yet people with ME/CFS are historically misunderstood. There remain many gaps in clinical knowledge regarding causes and treatments for ME/CFS.

This said, it has long been theorised that ME/CFS - like long COVID - is a post-viral condition, meaning that it may be caused by an initial viral infection which triggers long-term symptoms that remain after the virus is gone. The existing research on ME/CFS is now being studied and revisited through the lens of long COVID.

By building on ME/CFS research and theorising connections, experts hope to avoid 'reinventing the wheel' and instead build a better understanding of both diseases and ultimately find effective treatments: "I think the tools we've applied to study ME/CFS can now easily be applied to long COVID as well. And vice versa," says Dr. Avindra Nath, clinical director of the National Institute of Neurological Disorders and Stroke (NINDS).

What is long COVID?

Long COVID is a newly recognised multi-system condition that results from a COVID-19 infection, although not everyone who contracts COVID-19 will develop long COVID. What sets long COVID apart from acute COVID-19 is that symptoms persist after the virus has left the body for more than four weeks after initial contraction of COVID-19.

Long COVID symptoms are wide-ranging, hugely variable in severity, and may disappear for periods at a time. They include:

What is ME/CFS?

ME/CFS is a long-term condition that causes extreme fatigue alongside other symptoms. In the UK, ME/CFS is believed to affect between 1 and 5 people in every 1,000; however, as the condition often goes undiagnosed, the true figure may be higher.

Main symptoms of ME/CFS include:

  • Excessive fatigue - which, importantly, is not relieved by rest.
  • Cognitive difficulties.
  • Post-exertional malaise.
  • Sleep disturbances.

ME/CFS may also cause:

Long COVID and ME/CFS shared symptoms

A significant amount of people infected with COVID-19 who develop long COVID are dealing with fatigue that's so debilitating that it warrants an ME/CFS diagnosis. Some studies suggest this figure is 40%, and figures from the Office for National Statistics show that fatigue is the most common symptom experienced by people with long COVID, affecting 54% of people with the condition.

According to research, the most frequent shared symptoms of people with long COVID and people with ME/CFS are fatigue, cognitive difficulties, and post-exertional malaise (PEM).

Both post-viral syndromes that "overlap"?

Long COVID is proving difficult to understand because it is a complex, multisystem condition. One solid definition we have is that it is a post-viral (also called post-infectious) syndrome - we know that it follows infection from COVID-19.

But this is just one of four syndromes that is used to define long COVID:

  • A post-viral syndrome with overlaps with ME/CFS.
  • Debility (physical weakness) as a result of being seriously unwell with COVID-19 (so-called post intensive care syndrome).
  • Organ damage.
  • A new condition unknown until the pandemic.

While the cause of ME/CFS has not been proven, a popular theory is that the condition is also post-viral. After all, fatigue has long been recognised as a short-term symptom following some viral infections, such as glandular fever.

According to ME/CFS organisation Health Rising, COVID-19: "Is simply demonstrating in spades what's been known and ignored for years - that infections can, even after they've been "resolved", have severe long-term consequences."

Research has identified promising similarities

In August 2021, researchers at the annual International Association for Chronic Fatigue Syndrome/Myalgic Encephalomyelitis (IACFS/ME) conference came together to discuss their findings on the intersection between ME/CFS and long COVID.

Many similarities were discussed:

  • Both diseases may be due to an immune system response caused by resistance to a virus.
  • This is indicated by vascular (blood vessel) injuries. Damaged endothelial cells lining the blood vessels may be affecting blood flow, causing inflammation, and triggering sympathetic nervous system activation, which may cause the common shared symptoms.
  • This may be damaging the neurons in the brainstem (a brain organ) in both conditions.
  • The ME/CFS symptoms of breathing difficulties and hyperventilation were found in 88% of long COVID study participants.

Points of difference were also found:

  • Cognitive difficulties are caused by problems with the nervous system and are a shared symptom of long COVID and ME/CFS. Compared to ME/CFS, the long COVID study participants found most cognitive symptoms to become less severe over time.

However, because the similarities relating to the cause of both conditions are so promising, study leader Dr. Leonard Jason argues that differences in symptom patterns "over time might contribute to helping better understand the pathophysiology of those reporting prolonged illness following COVID-19".

The importance of ME/CFS research for long COVID

While the surge of new research comparing long COVID and ME/CFS is promising for the future, existing ME/CFS knowledge has already proven hugely useful to many people with long COVID.

There is no known cure for ME/CFS, but for some patients, symptoms can be improved with support and advice that includes lots of rest, not using more energy than necessary, following a healthy diet, and drinking plenty of water. Symptoms management guidance and resources have been passed on by the ME Association to people experiencing long COVID who don't know where else to turn.

It would appear that people with long COVID have experienced positive results by adopting the energy management and lifestyle strategies that the ME/CFS community has promoted for years.

The importance of long COVID research for ME/CFS

The flurry of research into the long COVID crisis is being seen by the ME/CFS community as a significant opportunity to dramatically advance our knowledge of ME/CFS. Despite the connection with viral infections, the exact cause remains unclear because it is possible that not all cases of ME/CFS are triggered by a virus.

Now, as lots of illuminating data continue to come out of long COVID research, new insights into both conditions could mean better treatments are found. This has the potential to benefit the millions of lives severely affected by ME/CFS every day.

Future progress

After the first government-funded long COVID studies, Health Rising hopes to see many more large cohort studies as well as new cutting-edge technology that builds a picture of ME/CFS, long COVID, and many autoimmune disorders as well.

The House of Lords has highlighted the need for GPs to feed into this data collection drive. They call for GPs to follow up with patients with suspected long-COVID and to determine whether those with ongoing extreme fatigue meet the diagnostic criteria for ME/CFS. Not only will this mean that patients are directed to the most appropriate support, but this will also dramatically improve the data on the rates of ME/CFS in long COVID patients.

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