The Government is facing fresh calls to compensate frontline workers who are suffering from the long-term effects of coronavirus.

The All-Party Parliamentary Group (APPG) on Coronavirus has urged Prime Minister Boris Johnson to recognise long Covid as an occupational disease.

Here is what we know so far about the still-developing, ever-changing condition:

– What is it?

Long Covid, also known as post-Covid syndrome, is used to describe the effects of the virus that continue for weeks or months beyond the initial illness.

Guidelines from the National Institute for Health and Care Excellence (Nice) define long Covid as “signs and symptoms that develop during or following an infection consistent with Covid-19 which continue for more than 12 weeks and are not explained by an alternative diagnosis”.

The condition is associated with a range of symptoms, from fatigue and breathlessness to anxiety and depression.

– How widespread is long Covid?

One in five people who tested positive for coronavirus have gone on to develop longer-term symptoms, according to the most recent estimates.

Data from the Office for National Statistics published in December 2020 suggested around 186,000 people suffer problems for up to 12 weeks.

But research also suggests many patients with long Covid have been unable to properly return to work six months after infection.

Anecdotal evidence indicates children can be susceptible to long Covid as well as adults.

However, there has not been time to glean meaningful data, and long-term research into the condition is continuing.

– What are the symptoms?

According to Nice, long Covid usually presents with clusters of symptoms which may change over time and can affect any system within the body.

Lasting symptoms can include fatigue, breathlessness, anxiety and depression, palpitations, chest pains, joint or muscle pain, and not being able to think straight or “brain fog”.

The US Centres for Disease Control and Prevention (CDC) also has a list of reported symptoms, which include inflammation of the heart muscle, lung function abnormalities, acute kidney injury and rashes, as well as neurological complaints, such as taste, smell and concentration issues.

Such a wide range of symptoms and different presentations of illness make it hard for doctors to diagnose and treat the condition.

Scientists from the UK’s National Institute for Health Research (NIHR), who reviewed the available evidence of the symptoms in October 2020, believe ongoing Covid may not be one illness but at least four different syndromes.

– What is the cause?

Medical experts are still trying to figure out what causes long Covid.

Sars-CoV-2, the virus that causes Covid-19, can trigger an overactive immune response which also causes damage throughout the body.

Some believe the immune system does not return to normal after Covid-19 and this could be one of the reasons for prolonged ill-health.

One US study suggested low hormone levels in patients is a likely link to long Covid.

Meanwhile, in research published in the Lancet in November 2020, scientists in Italy found major structural changes in the lungs of patients who died with Covid-19.

– Who is at risk of long Covid?

Long Covid is not just people taking time to recover from severe disease.

Reports suggest that even those with relatively mild infections can experience lasting health problems.

Researchers from the NIHR have said it cannot be assumed that people who are at lower risk of severe illness and death from Covid-19 are also at low risk of long Covid.

They said more work is needed to help those who are suffering, adding that many are “not believed” when they seek help.

– What is being done about it?

England now has nearly 70 clinics to address long Covid, harnessing doctors, nurses, physiotherapists and occupational therapists to offer physical and psychological assessments and refer patients to the right treatment and rehabilitation services.

Nice has also published official guidance on best practice for recognising, investigating and rehabilitating patients with long Covid.

Developed with the Scottish Intercollegiate Guidelines Network (Sign) and the Royal College of General Practitioners (RCGP), the guidelines will be updated as new evidence relating to long Covid emerges.

Those worried about their symptoms four weeks or more after having coronavirus can contact their GP, who may recommend blood tests and a chest X-ray as part of the investigation.

The NHS also has a Your Covid Recovery plan, which contains advice, particularly for those who needed hospital treatment, and is available at https://www.yourcovidrecovery.nhs.uk/