(London) Ongoing illness after infection with COVID-19, sometimes called "long COVID", may not be one syndrome but possibly up to four causing a rollercoaster of symptoms affecting all parts of the body and mind, doctors said on Thursday.

In an initial report about long-term COVID-19, Britain's National Institute for Health Research (NIHR) said one common theme among ongoing COVID patients - some of whom are seven months or more into their illness - is that symptoms appear in one physiological area, such as the heart or lungs, only to abate and then arise again in a different area.

"This review highlights the detrimental physical and psychological impact that ongoing COVID is having on many people's lives," said Dr Elaine Maxwell, who led the report.

Many thousands of people worldwide have linked up on social media platforms and online forums to share their experiences of ongoing COVID-19 symptoms. Some call themselves "long haulers" while others have named their condition "long COVID".

According to UK-based patient group LongCovidSOS, data from a King’s College London-devised symptom tracker app shows that 10% of COVID-19 patients remain unwell after three weeks, and up to 5% may continue to be sick.