Although the exact prevalence of ME/CFS is unknown, several estimates exist both for the UK and elsewhere in the world. While not an exhaustive review of all studies containing information on ME/CFS prevalence (which would need to be a specific type of study that uses repeatable methods to search for, select, and combine all available evidence to answer a specific question; i.e. a systematic review), the following summarises key prevalence estimates, alongside the strengths and limitations of the methods used to calculate them.
Existing estimates for the UK – what do government reports and guidelines say?
The most frequently used estimate for the prevalence of ME/CFS in the UK is probably that cited in the information to the public relating to the 2021 NICE guidelines for diagnosing and managing ME/CFS, this states that ME/CFS:
“affects about 250,000 people in the UK”
However, even within the NICE guideline, inconsistency in the prevalence of ME/CFS can be observed; in the guideline itself – rather than the information to the public – it is stated that:
“Recent data from the UK Biobank suggest that there are over 250,000 people in England and Wales with ME/CFS, with about 2.4 times as many women affected as men.”
This estimate of 250,000 people with ME/CFS came from research, published in 2018, using data from the UK Biobank – “a large-scale biomedical database and research resource containing de-identified genetic, lifestyle and health information and biological samples from half a million UK participants”.
Findings showed that among 452,264 individuals in the UK Biobank, 1,829 people self-reported “CFS” – corresponding to a prevalence of 0.448%. Regrettably, the cases of CFS were self-reported and not assessed against any ME/CFS diagnostic criteria. Additionally, the UK Biobank data lacks ethnic diversity and only includes adults aged between 40 and 69 years between 2006 and 2010. These limitations mean that it may not be appropriate to extrapolate the prevalence of 0.448% to the wider UK population, as was done in the 2021 NICE guidelines.
Prevalence estimates also exist for Scotland and Northern Ireland:
A report from the Scottish Government on “Myalgic Encephalomyelitis/Chronic Fatigue Syndrome NICE guideline: stakeholder review” published in July 2022, stated that:
“Around 20,000 people in Scotland are living with the condition.”
Information from the “ME/CFS in Northern Ireland Position Statement as at 31 August 2016” suggests that:
“Specifically, there are more than 7,000 cases in Northern Ireland, with 10% of patients suffering from moderate to severe symptoms.”
While it is unclear exactly where the estimates for Scotland and Northern Ireland are obtained from, there is a reference to the idea that “a population prevalence of at least 0.2% to 0.4% is widely accepted” in the 2022 report from the Scottish Government – this range was also cited in another report from the Scottish Government first published in 2010, and updated in 2023. Regrettably, the position statement from Northern Ireland references a web page that can no longer be accessed.
Prevalence figures were also in circulation before the 2021 NICE guideline. The 2006 Gibson Report (Inquiry into the status of CFS / M.E. research into causes and treatment) quoted that the Chief Medical Officer’s (CMO) Report of 2002 stated:
“There could be anything from 100,000 to 250,000 people suffering from CFS/ME in the UK.”
Both the CMO Report of 2002 and the 2007 NICE guideline for ME/CFS utilised “a population prevalence of at least 0.2% – 0.4%” – although, again did not provide a clear reference for this range (it is possible that the justification in the CMO report was published in an Annex which is no longer available online via the link provided in the report).
Although 0.2% to 0.4% is a wide range, it was considered by some as a “low estimate” and, of course, does not and could not predict the impact of long COVID on potential numbers of those capable of receiving a diagnosis of ME/CFS.
Considering a prevalence of 0.2% to 0.4% and applying it to the UK population at dates of quoted reports and guideline release dates:
| Year | Population | 0.2% of population | 0.4% of population |
| 2002 | 59,365,677 | 118,731 | 237,462 |
| 2006 | 60,827,067 | 121,654 | 243,308 |
| 2007 | 61,319,075 | 122,638 | 245,276 |
| 2021 | 67,026,292 | 134,052 | 268,105 |
There have been no more recently published reports or guidelines that include information on the prevalence of ME/CFS in the UK. Thus to 2007, the 0.2% to 0.4% rate would, at the highest limit, be in accord with the 250,000 figure, but as population figures have risen the crude population range has exceeded 250,000; if the range of 0.2% to 0.4% is applied to the most recent population estimate for the UK – 68,265,200 people in 2023 – it would equate to between 136,512 and 273,025 people.
What does the research tell us?
Since the UK Biobank study in 2018 – the study cited by NICE in 2021 as a reference for the 250,000 figure – there has only been one peer-reviewed study, funded by ME Research UK, which estimates the prevalence of ME/CFS in the UK. This study used hospital records from England and counted the number of cases of ‘post-viral fatigue syndrome’ (ICD code G93.3) – the diagnosis with symptoms most closely matching those of ME/CFS. Results suggested that on the 7th October 2023, 100,055 people in England – 0.16% of the 62,782,175 individuals in the study – had been diagnosed with the ICD code G93.3.
In the discussion section of the paper, the authors take the G93.3 prevalence rates for males and females facing the least barriers to diagnosis in England (0.25% for males and 0.92% for females) and extrapolate them to the UK population size for 2023 of 68.3 million people. This calculation suggests that if the prevalence rates for England apply to all people in the UK, 83,626 males (0.25% of 33.450 million males in the UK) and 320,296 females (0.92% of 34.815 million females in the UK) would be given a G93.3 diagnosis in their lifetime; i.e. 403,922 people in total. This would equate to a prevalence rate of approximately 0.6% – 62% higher than the previous estimate of 250,000 people with ME/CFS quoted in the 2021 NICE guidelines for the diagnosis and management of the disease
Before this, a systematic review by Lim and colleagues, which included all research relating to the prevalence of ME/CFS published between 1990 and 2018, suggested that research using populations from the UK (not all UK-wide studies) provided a ME/CFS prevalence range of between 0.1% and 2.62% for the UK (another systematic review by Estévez-López and colleagues published in 2020 identified that this range was 0.1% to 2.2% in Europe between 2002 to 2011).
Importantly, research published before 2018 has identified that prevalence rates for ME/CFS differ depending on which criteria are used. For example, the systematic review of international evidence by Lim and colleagues suggested that the prevalence of ME/CFS could lie anywhere between 0.04% (the lower range when considering evidence relating to the “Canadian Consensus Criteria; Epidemiological case definition; Post-viral exhaustion syndrome; and the National Institute for Health and Care Excellence guideline 2007”) and 12.55% (the upper value based on the Australian diagnostic criteria).
Elsewhere in the world:
- A peer-reviewed study in Australia identified a prevalence rate of 0.095% for “A diagnosis of “myalgic encephalomyelitis”, “chronic fatigue syndrome”, “ME”, “CFS”, or “ME/CFS” but recognised that this was likely to be an underestimation due to delays in diagnosis and lack of interaction with health professionals.
- A pre-print study in Canada suggested a prevalence of 0.4% for “confirmed cases of ME/CFS”, and 1.1% for self-reported cases of “CFS”.
- A report by the Centers for Disease Control in the USA, published in 2023, found a prevalence of 1.3% for self-reported diagnosis of ME/CFS.
- Peer-reviewed research from the USA, led by Mariah Wood and published in 2024, identified that among 2,745,374 adults in 2022, 45,892 (1.67%) reported symptoms consistent with the 2015 IoM criteria for ME/CFS – something the authors termed “ME/CFS-like illness”.
What about the impact of long COVID?
Due to the overlap in symptoms between ME/CFS and long COVID, it is essential to consider how the COVID-19 pandemic may have affected the prevalence of ME/CFS. Overall, research suggests that although ME/CFS may be no more common following COVID-19 than other infections, the number of people who contracted COVID-19 – and then developed long COVID – may mean that the number of those meeting ME/CFS diagnostic criteria (i.e. the prevalence of ME/CFS) has increased:
- Research from Mariah Wood identified that 14.2% of the 45,892 adults in the USA who reported symptoms consistent with the 2015 IoM criteria for ME/CFS (or had ME/CFS-like illness”) developed the illness following COVID-19 infection.
- Another study (behind paywall) from the USA by Mirin and colleagues, published in 2022, used existing ME/CFS prevalence estimates and concluded that if 10% of those with long COVID met ME/CFS diagnostic criteria, the prevalence of “ME/CFS” in the USA may have increased from 1.49 million to between “5 and 9 million individuals” – based on the 2022 population for the USA of 341.5 million, this would equate to approximately 1.46% to 2.64%, which includes the 1.67% observed by Wood and colleagues.
- One additional pre-print study, which has been published ahead of peer review, considered the the number of people who met either the CCC or IoM for ME/CFS 6-8 months following COVID-19 infection. The researchers looked at two different cohorts; 217 adults in the John Hopkins University (JHU) COVID recovery cohort, and the 388 adults in the long term Impact of Infection with Novel Coronavirus (LIINC).
- Results suggested that in the JHU cohort, 97 (45%) of participants met the study definition for long COVID – of these, 5 (5.2%) met IoM criteria for ME/CFS, and 2 (2.1%) met the CCC – it is important to note that the majority of these individuals were also living with HIV.
- In the LIINC cohort, 281 (72%) adults met the study definition for long COVID, 51 (18.2%) of these met the IoM criteria for ME/CFS, and 29 (10.3%) met the CCC – few of these people were living with HIV.
- Also of relevance, is a systematic review – a type of study that uses repeatable methods to search for, select, and combine all available evidence to answer a specific research question, has been published and concluded that 51% of people with long COVID met ME/CFS diagnostic criteria. However, in a letter to the editor of the Journal of Infection, Nuno Sepúlveda and Francisco Westemeier highlight several potential methodological issues with the systematic review that may mean that the main finding is – that approximately 50% of people with long COVID meet ME/CFS criteria, is likely to be an overestimation that can be explained by “biased samples” recruited from long COVID support groups.
Summary
While it is possible to use existing estimates for ME/CFS prevalence and apply them to the UK population of today – as done in the study by Gemma Samms and Chris Ponting – there are limitations of taking these existing estimates and extrapolating to a different population. For example, these estimates do not capture differences in population structure due to factors such as age, rurality, and socioeconomic status. The next article in this series will explore these limitations in more detail.
For more information on the limitations of studies included in this article, please read “Additional information on the studies relating to the prevalence of ME/CFS“
What is prevalence? | Additional information | Difficulties with prevalence estimates | Summary
