WHO also said today that it was advising the use of a pulse symmetry to measure oxygen levels of Covid patients at home to see if they are deteriorating and need hospitalisation.

The World Health Organization issued fresh clinical advice today for treating Covid-19 patients, including those displaying persistent symptoms after recovery.

A study by the Office for National Statistics in the UK estimated that one in five people has symptoms that persist after five weeks, and one in ten has symptoms for 12 weeks or longer after acute coronavirus infection.

An article published in The Lancet medical journal last month by healthcare workers affected by long Covid listed ongoing symptoms including renal impairment, new-onset diabetes and lung disease.

WHO also said today that it was advising the use of a pulse symmetry to measure oxygen levels of Covid patients at home to see if they are deteriorating and need hospitalisation.

The agency is recommending using low-dose coagulants to prevent blood clots and said it has "not seen definitive evidence of a change in the virus except in terms of transmissibility".

WHO spokeswoman Margaret Harris, attending a UN briefing in Geneva, declined to comment on reports of delays in roll-out f vaccines in the European Union.

She said she had no specific data and the WHO's priority was for health workers in all countries to be vaccinated in the first 100 days of the year.

Ms Harris said a WHO-led team of independent experts, currently in the central Chinese city of Wuhan where the first human cases were detected in December 2019, is due to leave quarantine in the next two days to pursue work on the virus origins.

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