Health experts have been baffled by the condition which is said to have impacted more than one million people across the UK.
In a paper titled “A clinical case definition of post-Covid 19 condition” describes so-called long Covid as something that occurs in individuals that have come down with the virus.
WHO says that the ‘post Covid-19 condition’ usually happens three months after onset Covid, with symptoms lasting for at least two months, the Mirror reports.
Common symptoms of long-Covid include fatigue, shortness of breath and cognitive dysfunction.
The condition should be diagnosed if the symptoms “cannot be explained by an alternative diagnosis”, the paper reads.
It adds that coming up with a definition is an important first step to ensure that health officials can spot and treat the condition as effectively as possible.
The WHO said a separate definition may be applicable for children.
It comes as 1.1million people in the UK are estimated to be experiencing self-reported Long Covid, according to the data from the Office for National Statistics.
The ONS data is for the four weeks to September 5, which is up from 970,000 in the previous survey.
It comes as the UK currently has 66,033 new symptomatic cases of Covid with the virus being most prevalent among children between 10 and 19-years-old, a new study has shown.
According to figures released by the ZOE COVID Study App, the total number of cases this week is up 13.6 per cent from 58,126 last week.
Experts have warned of the risks of allowing for the virus to “run rampant” among groups of young people aged between 10 and 19, where cases are surging the most.
A total of one in 30 are currently infected with Covid in this age group.
Professor Tim Spector, lead scientist on the ZOE COVID Study app, commented on the latest data saying “we can only hope that some kind of herd immunity will kick in and cases will drop”.
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