Severe cases of Covid-19 can leave sufferers with fatigue, sleep difficulties and hair loss, lasting weeks or even months after patients test negative.
Researchers in China followed more than 1,700 patients, in the original centre of the Covid-19 outbreak in Wuhan, to chart their recovery from the virus.
They found that about three quarters of them, 76 per cent, were still experiencing at least one symptom six months later.
The most common after-effects were fatigue or muscle weakness, which was experienced by almost two thirds, or 63 per cent.
A quarter suffered from sleep difficulties, while one in five experienced hair loss.
Other enduring symptoms included a smell disorder in 11 per cent of patients, while 9 per cent felt palpitations and a similar number experienced joint pain.
Decreased appetite was reported by 8 per cent of patients; while 7 per cent said they had a taste disorder and 6 per cent felt dizziness.
Researchers also found 5 per cent of patients were experiencing diarrhoea or vomiting, and a similar proportion felt chest pains.
Less than 5 per cent of people were still suffering from a sore throat or finding it difficult to swallow; a skin rash; myalgia or a headache.
A low-grade fever was seen in fewer than 1 per cent of former sufferers.
"At six months after acute infection, Covid-19 survivors were mainly troubled with fatigue or muscle weakness, sleep difficulties, and anxiety or depression," said the researchers in the study published in medical journal, The Lancet.
The findings came after another study, this time from the UK, showed that almost a third of patients who recover from the infection return to hospital with symptoms within five months. One in eight of them died.
The study, by researchers at the University of Leicester and the Office of National Statistics, followed 47,780 people who were discharged from hospital. Of those, 29.4 per cent were readmitted within 140 days and 12.3 per cent died.
The UK study was the largest to follow people who were discharged after being admitted with the virus.
UAE residents tell of battle with "long Covid"
People who go on to suffer lasting effects of the virus are said to be suffering from “long Covid”, a mysterious condition with an unknown cause.
In December, The National told how Covid-19 was still affecting the lives of some residents several months after they were given the all-clear.
Eman Jamal was one such "long-hauler", beset by health issues more than eight months after catching Covid-19.
“I will be OK for sometimes an entire week at a time, and then suddenly I wake up with a breathing difficulty,” she said.
“I try to rest for a bit and then a couple of days later, I might feel better.”
Seema Mary Rajan, 39, a nurse working in Sharjah, also experienced continuing health problems since testing positive for the virus in May.
The Al Zahra Hospital employee said she felt constant pain in her joints for months before she was told a few weeks ago that she had osteoarthritis.
And because doctors do not know what is causing the condition, they cannot say how long its effects will last.
The effect is not limited to severe cases. Experts say even mild cases can make people sick for months.
Recent research from the UK found beating Covid-19 provides protection of about 85 per cent, which is comparable to many vaccines.
"Two things are important to understand, that still infections can occur, and immunity is not lifelong," said Dr Sunil Kumar Garg, a specialist in critical care medicine at NMC Royal Hospital, DIP, Dubai.
“It means once immunity wanes over the period of time, you are predisposed to infection as if you never had the infection.
“The good side of this is that if reinfection occurs, it is usually asymptomatic or mild state only.”
Experts said the best way for people to protect themselves from the virus is to follow precautions, and get vaccinated.