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Following months of uncertainty surrounding the symptoms of "long COVID", the World Health Organization (WHO) has now given it a formal definition 18 months into the pandemic.
The condition has remained one of the more mysterious aspects of coronavirus, but the WHO has sought to come up with a clinical analysis of the long-term symptoms more formally called the “post-COVID condition”.
Their official definition of long COVID is: “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.
Watch: COVID-19: More than one million people say they have long COVID, ONS data shows
“Common symptoms include fatigue, shortness of breath, cognitive dysfunction but also others... which 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 WHO added that providing a firm definition was important as it was the first step in ensuring health officials can spot and treat the condition has effectively as possible.
The WHO said that separate definition of long COVID may be applicable for children.
The definition comes as new data from the Office for National Statistics (ONS) showed that more than a million people in the UK are estimated to be experiencing self-reported long COVID.
Some 1.1 million people in private households have experienced long COVID during the four weeks to 5 September, the ONS said.
This is up from 970,000 in the previous survey and is the largest monthly increase since estimates of self-reported long COVID prevalence were first published in April.
Self-reported long COVID is defined as symptoms persisting for more than four weeks after their first suspected coronavirus infection that are not explained by something else.
The data also shows an estimated 405,000 people have experienced self-reported long COVID that has lasted for at least a year, up from 384,000 a month earlier.
The WHO said coming up with a formal definition for the condition was difficult as there were so many symptoms associated with it.
Mike Ryan, executive director of the WHO’s Health Emergencies Program, said that while the definition was a “great step forward”, it was likely to change as the condition evolved.
Last month, an ONS study found that long COVID was less common than first feared with one in 40 having coronavirus symptoms that lasted at least three months – significantly less than the one in 10 reported in April.
The NHS official guidance lists symptoms of long COVID as:
extreme tiredness (fatigue)
shortness of breath
chest pain or tightness
problems with memory and concentration ("brain fog")
difficulty sleeping (insomnia)
pins and needles
depression and anxiety
feeling sick, diarrhoea, stomach aches, loss of appetite
a high temperature, cough, headaches, sore throat, changes to sense of smell or taste
Watch: Coronavirus vaccine halves risk of long COVID, study finds