As many as nine in 10 people who are hospitalised with the coronavirus endure at least one symptom two months later, a report has revealed.
Not everyone who overcomes the infection returns to a clean bill of health, with some developing so-called long COVID, leading to complications like brain fog, palpitations and even organ damage.
With the coronavirus only identified at the end of 2019, long COVID is a relatively new phenomenon, and medics are somewhat in the dark about how best to treat its symptoms.
In its second report on the subject, a team from the National Institute for Health Research (NIHR) analysed more than 300 scientific papers from around the world.
Read more: Scientists get a grasp on long COVID's cause
It has reported that among those admitted to hospital with coronavirus complications, between 50% and 89% have at least one lingering symptom two months later.
Of those with a milder bout of the infection that did not require hospital care, 20% to 30% endure one or more symptom around four weeks on, while at least one in 10 (10%) still have long COVID three months later.
Watch: What is long COVID?
"This awful disease can lead to long-term symptoms affecting people's quality of life," said health secretary Matt Hancock.
"So it is vital we do all we can to improve our understanding of long COVID, and develop more effective care and treatments for people suffering from its impact.
"Today's report, on top of the £20m ($27m) research funding to support innovative projects and establishment of clinics across the country, will all help improve understanding and treatment of long COVID."
A recent government report revealed long COVID is more common among women, with females under 50 being over five times more likely to endure "incomplete recovery", a new disability or severe fatigue than their male counterparts.
The NIHR results similarly suggest that long COVID is more prevalent in women and "young people (including children) than might have been expected from acute COVID mortality".
Early research suggests the coronavirus is mild in four out of five cases, with the vast majority of deaths occurring among elderly patients.
Not everyone who develops long COVID had a severe bout of the infection itself, with some even being asymptomatic beforehand.
The NIHR team also reported that just under a third (30%) of coronavirus patients endure anxiety or depression one to three months after supposedly clearing the infection.
This comes after medics from Massachusetts General Hospital found that people who have headaches while infected with the coronavirus are more likely to endure depression down the line.
Of the 10% of coronavirus patients who still had symptoms three months later in the NIHR report, fatigue was the most common complaint.
"Limitations in the way data is collected mean this may not be a comprehensive reflection and we may see estimates increase," said Dr Elaine Maxwell, from the NIHR.
The government report found half of its participants did not feel fully recovered seven months after catching the coronavirus, of whom three-quarters had fatigue.
The NIHR team also detected organ damage among patients who were and were not hospitalised with the coronavirus.
In the government report, the participants who required invasive ventilation were four times more likely to endure an incomplete recovery.
The NIHR team's findings build on previous research that suggests long COVID is an "umbrella term" made up of four syndromes – post-intensive care unit syndrome; long-term organ damage; post-viral syndrome; and an entirely novel syndrome, which may be identified as long COVID.
"Indeed there is some recent evidence long COVID might be an active disease, with continued inflammatory responses, lingering viral activity and/or blood clotting disorders," wrote the team.
Professor Chris Whitty, England's chief medical officer and co-lead of the NIHR, added: "What we term 'long COVID' likely covers a range of syndromes, which will require different approaches.
"It is important we work out what exactly the various elements of long COVID are and then we can target research at these parts in order to prevent and treat it."
Watch: Do coronavirus vaccines affect fertility?
In addition to reviewing the scientific papers, the NIHR team also compiled a survey, completed by more than 3,000 long-COVID patients.
Four in five (80%) of the respondents said long COVID affected their ability to work, while just over seven in 10 (71%) claimed their family life had been impacted.
More than a third (36%) said the condition affected their finances, while 32% "had not been able to access all of the healthcare services they thought they needed".
"This second review takes us on from our first by focusing on a wide range of emerging evidence that simply didn't exist even six months ago," said Candace Imison, from the NIHR.
"Together with findings from our short survey for people living with long COVID, it provides a unique insight into the current state of play."
Existing treatment guidelines urge long COVID patients to pace themselves, set "realistic goals" and join support forums.
The condition is officially diagnosed as "signs and symptoms that develop during or following an infection consistent with COVID-19, continue for more than 12 weeks and are not explained by an alternative diagnosis".
"Management of long COVID has so far focused on ruling out other diagnoses, treating individual symptoms and rehabilitation, and access to services has been variable," said Dr Maxwell.
"Looking forward, we need to offer a holistic, integrated approach rather than symptom by symptom management.
"We recommend rapid evaluation of different service models and skill mix for supporting people with long COVID."