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Will the World Health Organization’s long COVID definition help or hinder?

The World ME Alliance has written to the World Health Organization (WHO) concerning their recently published definition of “post COVID-19 condition”, commonly known as long COVID.

While we commend the work undertaken to ensure people with long COVID are receiving a diagnostic label and subsequent support we remain concerned that a vague definition alone could hinder research and care efforts.

Further work, including stratification of sub-types is vital, and we call on the WHO to engage disease experts from areas such as ME in this.

Read our letter below:

Dear Dr Tedros Adhanom Ghebreyesus, Dr Ren Minghui and Dr Janet Diaz,

On 6th October, the World Health Organization published its definition of post COVID-19 condition (PCC).

Post COVID-19 condition occurs in individuals with a history of probable or confirmed SARS-CoV-2 infection, usually 3 months from the onset of COVID-19 with symptoms that last for at least 2 months and cannot be explained by an alternative diagnosis. Common symptoms include fatigue, shortness of breath, cognitive dysfunction but also others* and generally have an impact on everyday functioning. Symptoms may be new onset following initial recovery from an acute COVID-19 episode or persist from the initial illness. Symptoms may also fluctuate or relapse over time.

The undersigned organisations work for the benefit of people with myalgic encephalomyelitis (ME), a noncommunicable disease (NCD) with great experience of vague diagnostic definitions. There are now so many definitions of ME that research often isn’t comparable. Many of these definitions select such a broad population that research outcomes are considered of low or very low quality in systematic reviews. In fact, there is remarkable similarity between some of the definitions of ME and the recent definition of PCC published by the WHO.

We are concerned that this definition will lead to some of the same outcomes for people experiencing PCC as has happened for people with ME. Defined clinical pathways are clearly needed, and we commend the WHO on working towards this. However, now is the time to prioritise the categorisation of subtypes in order to expedite the delivery of appropriate treatment or management approaches for people presenting with different symptoms. As research into this novel phenomenon develops, various phenotypes are being differentiated, and the WHO definition could emphasise this. (1) In particular, it is of vital importance that post-exertional malaise (PEM) is screened for, and where present people are supported to pace their energy levels within known limits (as per new guidance from the UK’s National Institute for Health and Care Excellence). (2) The findings of the Patient Led Research Collaborative, that “89.1% of participants reported experiencing either physical or mental PEM”, (3) affirm this.

There are many overlaps between the symptomology presenting in PCC and in ME. However, certain subgroups do not experience the symptoms of ME. We must now ensure that people diagnosed with PCC are appropriately sub-categorised, to ensure that we do delay the advancement of scientific understanding through:

  • misleading data and insignificant findings in research
  • inappropriate one-size-fits-all care

It is critical to identify and track the disease progressions of different subtypes, including those with ME, to identify risk and resiliency factors when compared to those who recover from COVID and healthy controls. As written, this definition alone will be harmful to critical research in the field.

We strongly encourage the WHO to work with NCD disease experts in related fields to develop guidance for clinical care and researchers that enables screening and tracking of ME and other conditions related to PCC, and fully defines the subgroups and their differentiating/differential symptoms.

The WHO has an opportunity here to make a difference for people with PCC, those with ME, and other NCDs who for many years have been out of the spotlight and largely ignored.

We therefore urge you to work with ME organisations and disease experts to make a statement on the similarities between PCC and ME, and the necessary differences in management approach for those experiencing post-exertional malaise.

Secondly, we urge you to ensure ME organisations and disease experts are central to future efforts to develop clinical care and research into PCC.

And finally, we urge the WHO to initiate education and research into PEM, as it remains such a misunderstood and highly disabling characteristic.

With regards,

Sonya Chowdhury,

Chair of the World ME Alliance

On behalf of the World ME Alliance members:

  • Action for M.E.
  • ACAF – Associació Catalana d’Afectades i Afectats de Fibromiàlgia i d’altres Síndromes de Sensibilització Central
  • AMMES – The American ME and CFS Society
  • ANZMES – The Associated New Zealand Myalgic Encephalomyelitis Society
  • AQEM – Association québécoise de l’encéphalomyélite myalgique
  • Forward M.E.
  • #MEAction
  • Plataforma Familiars FM-SFC-SQM Síndromes de Sensibilització Central
  • Solve M.E.
  • The ME CFS Foundation South Africa
  • WAMES – Welsh Association of ME & CFS Support

(1) Estiri, Hossein, Zachary H. Strasser, Gabriel A. Brat, Yevgeniy R. Semenov, Chirag J. Patel, and Shawn N. Murphy. “Evolving Phenotypes of non-hospitalized Patients that Indicate Long Covid.” medRxiv (2021).

(2) NICE. “Myalgic encephalomyelitis (or encephalopathy)/chronic fatigue syndrome: diagnosis and management” Available at (2021)

(3) Davis, Hannah E., Gina S. Assaf, Lisa McCorkell, Hannah Wei, Ryan J. Low, Yochai Re’em, Signe Redfield, Jared P. Austin, and Athena Akrami. “Characterizing long COVID in an international cohort: 7 months of symptoms and their impact.” Available at SSRN 3820561 (2021).

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