There is growing concern over the number of people who believed they had shaken off Covid-19 finding they are struggling months later with debilitating side-effects, with some feeling totally wiped out.
These people are being called "long-haulers".
While death rates from the illness have fallen here and in other countries there is now clear evidence a significant number who are no longer infected can go on to feel unwell to varying degrees.
A common complaint is a debilitating lack of energy.
It is easier to explain in those who had severe illness in the acute phase and ended up in intensive care.
But it has also been reported in people who had a milder episode of Covid-19.
Dr Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases in the US, said: "It's extraordinary how many people have a post-viral syndrome that's very strikingly similar to ME or chronic fatigue syndrome.
"They just don't get back to normal energy or normal feelings of good health."
Doctors say it is not unusual that some people who experience respiratory illnesses, including viral pneumonia, can suffer after effects.
More research is needed but there seems to be a broad range of symptoms reported by a significant number of people after Covid-19.
They include breathlessness and heart problems, with smaller numbers reporting delusions, strokes, insomnia, kidney disease and mobility difficulties.
One study looked at 1,216 patients in hospitals in 69 countries around the world who had heart scans.
Slightly more than half of these patients showed signs of damaging changes to their hearts, affecting how they pumped blood.
Most of them had healthy hearts before getting Covid-19.
A further 13pc showed severe dysfunction in their heart.
Irish cardiologists have seen a number of people infected with Covid-19 go on to suffer myocarditis which can affect the heart muscle, reducing its ability to pump and causing rapid or abnormal rhythms.
Some people have described having a kind of 'brain fog' and experiencing problems trying to think clearly.
They can have a normal brain scan but still not feel right. It's unclear what is happening but it has been suggested it is similar to a post-viral fatigue related to inflammation in the body.
Because Covid-19 has been around for such as short time there is still a lot to learn by medics about the lasting effects.
It will only become clear over time and when the findings of more studies emerge and are confirmed.