It has no formal definition, and there's no test to diagnose it. In fact, it has no official name. Symptoms vary widely - there one day, gone the next – baffling scientists. It can be so debilitating that even climbing a flight of stairs can put a sufferer back in bed for days. This is the phenomenon that has become known as “long haul COVID", “post-COVID syndrome” or just “long COVID”, and it is being investigated in people across the globe.
Increasing medical evidence is showing that a growing number of people who contract COVID-19 continue to grapple with a range of post-viral symptoms months after infection. Even those who may have initially experienced a relatively mild illness have reported that they continue to experience lingering symptoms. Recovery is erratic, with continuing and even new symptoms that fluctuate in intensity.
Both anecdotal reports and a growing body of research suggest persistent fatigue, breathlessness, "brain fog" and muscle aches, among other chronic problems, are affecting people for some time after their infection has cleared. Many say this prolonged illness severely impacts their lives, often leaving them unable to cope with work or enjoy everyday activities.
The World Health Organization (WHO) has reported that symptoms may linger or recur for weeks or months on end, while some patients develop medical complications that may have lasting health effects.
Although figures on how many people are afflicted by so-called long COVID are still emerging, an analysis by the COVID Symptom Study, led by King’s College London, in which millions of people in the US, UK, and Sweden are using an app to self-monitor their symptoms, found that as many as one in 10 people infected with the virus have symptoms lasting beyond one month. It is not thought that people are infectious for the long period, but just suffer long-term effects.