We are seeing the emergence of a new medical condition that is called “post-acute ­Covid-19” or “long Covid”.

As yet, we have precious little ­information on it, but it’s there.

The classic picture of the syndrome is delayed recovery from an episode of Covid, which is severe but doesn’t require special hospital treatment.

In broad terms there are two kinds, the first being more serious because of the danger of clot formation, the second being more general with fatigue and breathlessness.

“Post-acute” is defined as longer than three weeks and it is “chronic” if it lasts longer than 12weeks.

It’s not uncommon.

A US study found more than a third (35%) of people were still ill 14-21 days after a positive test and approximately 10% of people in the UK have suffered prolonged illness after Covid.

Most recover spontaneously, though slowly, with a holistic approach of rest, symptomatic treatment and gradual increase in activity.

There’s a wide variety of post-acute Covid-19 symptoms, the most common being cough, low-grade fever, and fatigue, all of which may come and go. But also reported are shortness of breath, chest pain, headaches and the inability to concentrate.

There’s also confused thinking, muscle pains and weakness, gastrointestinal upset, rashes, loss of control of diabetes, depression and other mental health conditions. Many kinds of skin rashes are part of post-Covid, including blisters, hives and a kind of chilblain that appears on the extremities, the so-called Covid toe.

We still don’t know why some people take a long time to recover. It’s a complicated picture, possibly with persistent viraemia – viruses in the bloodstream – due to weak or absent antibody response, as well as ­inflammation and other immune ­reactions. Factors such as ­post-traumatic stress may also play a part.

SARS and MERS have long-term respiratory, musculoskeletal and mental symptoms and these have parallels with post-acute Covid-19.

While we are assimilating ­information on this new syndrome, it’s advised that symptoms are treated with paracetamol or non-steroidal anti-inflammatory drugs.

Monitoring physical recovery in post-acute Covid-19 patients is still an inexact science, but experts say ­over-investigation should be avoided.

Most have a gradual, if sometimes protracted, improvement in energy levels and breathlessness, aided by careful pacing and not expecting too much. It’s likely most will regain their strength within four to six weeks of being able to begin light aerobic ­exercise, such as walking or Pilates, gradually increasing in strength.

When returning to work, a phased return may be best.