"The real concern is the fact that there is a wide range of symptoms that change over time and often intensify and can affect any system of the body," TASS quoted him as saying.
In particular, we are talking about fatigue, coughing, shortness of breath, inflammation and damage to major organs, including the lungs and heart.
Recovering from COVID-19 could take weeks or months, Gebreyesus noted, with no exact number of people with long-term effects being determined.
He said that WHO is planning additional research to develop treatment standards aimed at accelerating recovery and preventing complications.
Earlier, a new anti-record was recorded for the daily increase in the number of cases of coronavirus infection in the world - 505,756.