COVID-19 | The World Health Organization (WHO) this week issued a definition for "long Covid," a term used to describe the persistent health problems that affect some survivors of Covid-19.

Scientists are still working to understand the syndrome. Here is what they know so far:

HOW DOES THE WHO DEFINE LONG COVID?

The WHO defines long Covid as a condition with at least one symptom that usually begins within three months from the onset of confirmed or probable infection with the coronavirus, persists for at least two months and cannot be explained by another diagnosis. Symptoms may start during the infection or appear for the first time after the patient has recovered from acute illness...