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How methodological pitfalls have created widespread misunderstanding about long COVID
  1. Tracy Beth Høeg1,2,
  2. Shamez Ladhani3,4,
  3. Vinay Prasad1
  1. 1Epidemiology and Biostatistics, University of California San Francisco, San Francisco, California, USA
  2. 2Clinical Research, University of Southern Denmark, Odense, Denmark
  3. 3Public Health England, London, UK
  4. 4St George's University of London, London, UK
  1. Correspondence to Dr Vinay Prasad, Epidemiology and Biostatistics, University of California- San Francisco, San Francisco, CA, USA; vinayak.prasad{at}

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Key messages

  • The existing epidemiological research on long COVID has suffered from overly broad case definitions and a striking absence of control groups, which have led to distortion of risk.

  • The unintended consequences of this may include, but are not limited to, increased societal anxiety and healthcare spending, a failure to diagnose other treatable conditions misdiagnosed as long COVID and diversion of funds and attention from those who truly suffer from chronic conditions secondary to COVID-19.

  • Future research should include properly matched control groups, sufficient follow-up time after infection and internationally-established diagnostic or inclusion and exclusion criteria.


High rates of long COVID or post-acute sequelae of COVID-19 (PASC) continue to be reported in academic journals and subsequently filtered to the public. For instance, the Centers for Disease Control and Prevention (CDC) recently stated ‘nearly one in five American adults who have had COVID-19 still have long Covid’.1 Many scientific publications overestimate PASC prevalence because of overly broad definitions, lack of control groups, inappropriate control groups, and other methodological flaws. This problem is further compounded by inclusion of poorly conducted studies into systematic reviews and meta-analyses that overstate the risk. This is fed to the public by the media and social media, raising undue concern and anxiety. This paper aims to discuss these estimation errors and why epidemiologic research on long COVID has been misleading.

The problem with current case definitions

For the purposes of this paper, we define long COVID as a syndrome or individual symptoms which are direct sequelae of the virus, SARS-CoV-2, and last at least 12 weeks. Some post-COVID sequelae such as post-ICU syndrome, and post-pneumonia respiratory compromise are common to many upper respiratory viruses. While post-infectious conditions common to other respiratory illnesses may be included in estimates of prevalence of lasting symptoms, we propose future research avoid the umbrella term ‘long COVID’ and …

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