An England-wide network of almost 70 specialist clinics has been established to help people suffering from the long-term effects of the coronavirus, or long Covid.

The problem is continuing to cause serious issues worldwide for many who felt they were in the clear once said to have been recovered from Covid-19.

Here’s what we know so far in the still-developing, ever-changing picture of the condition.

– What is it?

Long Covid, the name applied so far by experts grappling with the issue of longer-term effects of the coronavirus. The latest official guidelines in Britain use two definitions: people may have “ongoing symptomatic Covid-19” if symptoms persist from four to 12 weeks, and could have “post-Covid-19 syndrome” if they do not resolve after 12 weeks.

But terminology across the world has changed frequently, with experts reshaping their definitions of what long Covid is from month to month.

Research early in the pandemic was by necessity focused on respiratory problems. The question of longer-term effects has been the target of increasing study in recent months, but medical experts know it is impossible to definitively say “this is long Covid” until a length of time has passed in which accurate, reliable patterns have emerged. This could take anything from a year, to three years, or longer.

In general, so much is still not reliably known about Covid-19 and its long-term effects – which is why you really do not want to contract it, no matter how old you are.

– How widespread is long Covid?

The NHS says one in five people who have contracted coronavirus have gone on to develop longer-term symptoms. It has data showing 186,000 have reported having problems for up to 12 weeks.

But there is also evidence so far, including cases documented in the US, where symptoms have continued for more than six months.

The big problem, again, is there has not been time to glean meaningful data from long-term studies of the condition. Showing the vagaries, early research in the US has suggested anywhere between 10% and 88% of Covid-19 patients will have one or more symptoms for many weeks – or months.

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

– What are the symptoms?

There are many, with NHS England saying the main ones seen in patient referrals have included anxiety, depression, breathlessness, fatigue and other debilitating problems.

But in information presented to a two-day seminar on long Covid held by the US National Institutes of Health (NIH) earlier this month, the US Centres for Disease Control and Prevention (CDC) listed 62 reported symptoms.

The most common echoed those on the NHS shortlist, and the top 10 also included tightness of the chest (No 2), chills and sweats, body aches, a dry cough, temperatures, headaches and a problem which has made returning to work difficult for many – brain fog. One American study showed 50% of non-intensive care Covid patients reported a significant change to their cognitive functioning.

The CDC has listed among the more serious effects inflammation of the heart muscle, lung function abnormalities, acute kidney injury and rashes, as well as neurological (such as taste, smell and concentration issues) and psychiatric (anxiety, depression, mood changes) complaints.

Also on the list were blood clots, hair loss, dizziness, trouble sleeping, loss of appetite, nausea, loss of smell and taste, sinus pain, extreme thirst, short-term memory loss, a burning sensation in the lungs, hallucinations and lucid dreaming, acne flare-ups and many more.

But it seems it does not stop there.

Also in America, the Patient-Led Research Group – a team of researchers who are also Covid-19 patients – ran a survey of 640 long Covid patients and recorded more than 200 total symptoms, also including testicular pain, urinary problems, menstrual changes, strokes and seizures. Many women reported their symptoms were worse just before their period. Both men and women reported sexual and reproductive system symptoms.

– What is the cause?

This is the major problem – so much is not known yet. At its recent seminar, the NIH concluded there were still far more questions than answers about long Covid – including extreme difficulties in predicting whose symptoms might linger, for how long and how best to treat them.

One US study suggested low hormone levels in patients was a likely link to long Covid. A German study found a majority of men admitted to hospital with Covid-19 had low testosterone levels. Another in Italy also predicted worse outcomes for coronavirus patients with low testosterone levels.

Such signs are helpful, but again, much remains unknown. For example, current advice in Britain says it is not known whether over-the-counter vitamins are helpful, harmful or have no effect in treating the condition.

The US seminar this month also heard doctors had been surprised by the scope of long Covid and its possible socio-economic impacts – comments that suggested coronavirus would continue to plague societies in various ways despite improved treatments, better preventative planning and the recent emergence of vaccines.

– What is being done about it here?

England now has 69 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. A further 12 sites are due to launch in January.

The National Institute for Health and Care Excellence (Nice) is also due to issue 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.