Watch: What is 'long COVID'?

While the confirmed global coronavirus death toll has exceeded 1 million, early research suggests four out of five cases are mild, with some people experiencing no symptoms at all.

The elderly and those with pre-existing health conditions – like diabetes, heart failure and kidney disease – are most likely to become seriously ill with the infection itself, however, a phenomenon called long COVID appears to be less discriminatory.

Long COVID, which is said to affect as many as 60,000 people in the UK alone, describes a range of complications that linger after a person tests negative for the coronavirus.

Read more: Long COVID patient 'not the same person she was'

It is increasingly emerging that some people with a mild bout of the infection are going on to develop long COVID. Medics have stressed this highlights the importance of adhering to social distancing, wearing face coverings and hand washing, regardless of your age.

While long COVID is poorly understood, some fear the somewhat mysterious complications may be worse than the infection itself for certain individuals.

What is long COVID?

Long COVID started as a fairly colloquial term, with the NHS instead acknowledging the “long-term effects of coronavirus”.

Post-viral fatigue can theoretically occur after fighting off any virus.

It is generally acknowledged, however, that the complications some are experiencing after overcoming the coronavirus are substantially more serious.

Most people recover from severe coronavirus symptoms within two to six weeks, however, for some complications appear to be lingering for months, even if they had only mild discomfort to start off with.

Patients enduring persistent symptoms known as long COVID are not infectious to others.

Read more: Two in five psychiatric ward patients had coronavirus at height of outbreak

The coronavirus was only formally identified on 31 December 2019. While scientists are learning more about the virus every day, how it affects patients long term is still somewhat of a mystery.

Many believe long COVID occurs when a patient’s immune system over-reacts to the infection, causing an excessive release of immune-fighting proteins, known as a cytokine storm.

This can lead to widespread inflammation that theoretically affects any organ.

It has also been suggested the virus may linger in “small pockets” of the body.

“If there’s long-term diarrhoea then you find the virus in the gut, if there’s loss of smell it is in the nerves; so that could be what's causing the problem,” Professor Tim Spector from King's College London told the BBC.

What are the symptoms?

Long COVID’s symptoms seem to be both vast and varied.

Many patients complain of debilitating fatigue, often so severe they struggle to work, walk up the stairs or even get dressed.

Dr Anthony Fauci, director of the US National Institute of Allergy and Infectious Diseases, has said an “extraordinary” number of survivors develop symptoms that are “strikingly similar” to chronic fatigue syndrome.

Breathlessness is also commonly being reported.

One of the main complications of the coronavirus is pneumonia, which comes about when the infection spreads to the air sacs in the lungs.

These then become inflamed and filled with fluid or pus, making it difficult to draw in air. In some cases, injured lung cells may be replaced by inflexible scar tissue.

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Doctors have said tens of thousands of coronavirus survivors in the UK will need to be called back to hospital to check for pulmonary fibrosis; lung scarring that can make day-to-day life a struggle.

Between 20% and 60% of people who overcame fellow coronavirus strains, severe acute respiratory syndrome (Sars) and Middle East respiratory syndrome (Mers), are said to have experienced a health problem similar to pulmonary fibrosis.

Heart palpitations, a risk factor for cardiovascular disease, have also been flagged.

Scientists from the University of Texas in Houston warned “the high inflammatory burden” of the coronavirus may lead to “significant cardiovascular complications”.

“Many viruses can affect the heart muscle as well as the lining around the outside of the heart that lubricates the heart's movement,” Professor Robert Storey from the University of Sheffield said in March.

“However, there is accumulating evidence that [the coronavirus] is associated with a higher risk of heart muscle damage than most common viruses.

“This may partly relate to entry of the virus into the heart muscle cells and partly to the overwhelming inflammation that some patients experience, which can injure the heart muscle.”

The coronavirus has even been linked to brain damage. A small study by University College London found a “higher than expected number of people” showed signs of injury to the vital organ, with these patients not necessarily having severe respiratory symptoms.

One expert has warned it “remains to be seen” whether the coronavirus causes similar brain damage as Spanish flu. The 1918 pandemic left some patients enduring viral encephalitis, brain swelling that can occur if an infection enters the central nervous system.

Read more: How to swab a baby, toddler or child for coronavirus at home

Some Spanish flu survivors also went on to develop viral Parkinsonism, defined as symptoms similar to Parkinson’s disease, like shaking and stiff movements.

As if all this wasn’t enough, scientists from the University of Manchester found more than one in 10 (13.2%) coronavirus survivors complained their hearing was worse eight weeks after being discharged from hospital.

While children generally overcome the coronavirus unscathed, a team from Imperial College London also raised concerns the infection may trigger type 1 diabetes in youngsters, after around twice as many young patients were diagnosed in a set period compared to the five-year average.

Although it is unclear why this may have occurred, the scientists speculated a protein on the coronavirus may attack insulin-producing cells in the pancreas.

Concerns were also raised when scientists from Great Ormond Street Hospital reported four coronavirus-positive children with widespread inflammation showed signs of brain damage.

This turned out to be temporary, however, with all the children improving and two making a full recovery within 18 days.

Coronavirus aside, patients who require intensive care often feel fatigued for up to 12 to 18 months. This is said to be due to lost muscle mass while spending a long time in bed.

How is it treated?

Being a new phenomenon, long COVID has no specific treatment guidelines.

Patients seem to be treated on a case by case basis, for example those enduring breathlessness may be prescribed an inhaler.

Not fully understanding the cause of long COVID makes treating the condition particularly tricky, doctors have said.

Medics may not be in the dark for long, however. NHS England and NHS Improvement have commissioned the National Institute for Health and Clinical Care Excellence (Nice) – a health watchdog – to develop a treatment guideline for long COVID.

The Scottish Intercollegiate Guidelines Network (SIGN) was given the same instruction by the chief medical officer of Scotland.

The guideline – expected by the end of 2020 – will provide a formal definition of the disease, tips on how to identify symptoms and a layout of the best treatment options to “support the management of the condition across diverse communities”.

“There is growing evidence to suggest COVID-19 is a multi-system disease that for many people involves persistent symptoms with longer term impacts on their health,” said Paul Chrisp, from Nice.

“It is important, therefore, that people requiring ongoing support and treatment are identified quickly and are supported by the NHS throughout every stage of their journey.

“We also want to ensure clinicians have clear guidance on how best to support patients struggling with this newly emerging disease.”

For now, the NHS’ Your Covid Recovery Plan recommends the three Ps:

• Pace yourself and get plenty of rest

• Plan your day so the most tiring activities are spread out across the week

• Prioritise what you need to do and what can be put off

How long may it last?

Perhaps frustratingly for long COVID patients, no one can accurately gauge how long their symptoms may last.

While medics hope the complications will ease over time, the mysterious nature of the condition means they could remain consistently unpleasant, or even get worse.

Many patients are undergoing tests and scans to uncover if their symptoms are the result of underlying organ damage, which could be permanent.

Perhaps reassuringly, a 15-year study by scientists from Peking University People’s Hospital in Beijing found Sars and Mers survivors with pulmonary fibrosis generally improved over time.

Watch: Long COVID - when the symptoms don’t stop