More research is still needed into the "constellation" of sometimes debilitating symptoms among people who have recovered from COVID-19, the World Health Organization said on Friday, noting that it will impact global health systems.

"We know that this post-COVID-19 condition - or as some patients also call it 'long COVID' and some clinicians call it 'long COVID' - is a heterogenous group of symptoms that occur after the acute illness", said Dr. Janet Diaz, Team Lead, Health Care Readiness at WHO.

"So, these are symptoms or complications that can happen potentially a month after, three months after, or even six months after, and as we are learning more, we are trying to understand the real duration of this condition."

Diaz noted that an unspecified number of sufferers had been unable to return to work, once they had recovered from the acute sickness caused by the new coronavirus.

"We are concerned obviously with the numbers of patients infected with SARS-CoV-2 virus that the numbers…just by the magnitude of the pandemic, will impact health systems."

By Friday, the number of COVID-19 infections globally had surpassed the 107.90 million mark with deaths exceeding 2.37 million, according to data from the Johns Hopkins University.

"What we know this far is that patients experiencing (a) post-COVID-19 condition could have been hospitalized patients, those in the ICU. So, we do know that has happened in patients who are very sick, but also in patients who were not managed inside the hospital…they have had complications and they have had persistent symptoms or new symptoms…or symptoms that waxed and waned, that came and went after their acute illness," said Diaz.

To promote a better understanding of post-COVID sickness and support patient care and public health interventions, the WHO has called on clinicians and patients to report data on symptoms to the Organization's Clinical Platform. 

"What we don't know is why it's happening, so what is the pathophysiology … of this condition…the researchers are really working hard to get to the answers of these questions," said Diaz.

(With input from UN)