The coronavirus pandemic has swept the globe for more than two years now, killing millions and infecting over half a billion people.
But while most patients recover quickly from their illness, some still feel the effects for weeks afterwards.
A recent study from the Office for National Statistics (ONS) estimates that up to 1.5 million people in the UK could be suffering from Long Covid.
Most people who catch Covid-19 recover quickly, but some suffer from ongoing symptoms after the initial infection for a few weeks, months, or even years and can be left with long term problems.
What is Long Covid?
Long Covid is the term used to describe the lingering symptoms of Covid-19 that last for weeks or months after the initial illness.
While there is no internationally agreed definition of Long Covid, the World Health Organisation (WHO) defines it as occurring usually three months from the onset of Covid-19, with symptoms that last for at least two months that can't be explained by an alternative diagnosis.
Healthcare professionals often refer to two types of Long Covid: ongoing symptomatic Covid-19, where ongoing symptoms persist for four to 12 weeks; and post-Covid-19 syndrome, where Covid symptoms persist for over 12 weeks.
Long Covid still isn't fully understood by healthcare professionals, with studies into why certain people develop long-term symptoms still ongoing.
Professor Amitava Banerjee, professor of clinical data science at UCL, is trying to gain a better understanding of Long Covid by leading the largest clinical study of the illness to date.
Speaking about the seriousness of Long Covid, he said: "We should be concerned, whether it's for young people and children, or for adults and older or more vulnerable people, with Long Covid there is a risk.
"When you think of 1.5 million [patients], that’s comparable to any long-term condition - that’s more than the number of people with dementia, that's more than the number of people with heart failure, so this is a really important threat to public health."
What are the symptoms of Long Covid?
Long Covid affects people in different ways and the signs and symptoms can vary. According to The National Institute for Health and Care Excellence (NICE) people with Long Covid usually develop a cluster of symptoms that often overlap, change over time and can affect any system in the body.
Some of the most common symptoms of Long Covid include:
- Brain fog, difficulty concentrating or memory issues
- Fatigue
- Chest pain
- Joint pain
- Muscle pain
- Shortness of breath
- Loss of smell or taste
- Persistent coughing
- A rapid heartbeat
- Difficulty sleeping
- Mental health issues, including anxiety and depression
People with certain risk factors, such as asthma, high blood pressure, or diabetes, are more likely to be severely ill with Covid-19, but the same can't be said about the likeliness of suffering from Long Covid symptoms. Even people who only suffer from mild Covid symptoms initially can develop Long Covid and suffer from serious long-term effects.
The severity of Long Covid symptoms also varies from person to person, and while some people may be able to manage their long Covid symptoms themselves, others will require the help of a healthcare professional.
How long does Long Covid last?
Most people will make a full recovery from Covid-19 within four weeks, but those who develop Long Covid can experience long-term effects for months, or in some cases even years.
The recovery time for Long Covid varies for everyone and the time it takes for Long Covid symptoms to disappear does not necessarily relate to the severity of the original infection.
Out of the 1.5 million people who reported suffering Long Covid symptoms as part of a recent ONS survey, 22% first had Covid less than 12 weeks earlier, 71% had Covid at least 12 weeks earlier, and 45% had Covid at least a year earlier.
Professor Banerjee recommends that people should still be trying to avoid catching Covid-19.
"There's an awful lot of people who have this for the long term, meaning months or maybe a year," he warned.
"We know that there's a reduced risk with vaccination but it's not totally protected and there's still research ongoing about what the impact of boosters is so I think the message is that avoiding infection with Covid should still be something that we’re pursuing."