Public health experts are divided over how many people are getting long COVID-19, a potentially debilitating condition that comes after a patient has recovered from the coronavirus.

Ill effects from the condition can include fatigue, pain, neurological issues and even changes in mental health.

Initially, public health officials believed that only a small minority of people would suffer from long COVID-19. But some studies now indicate a majority of those infected with the coronavirus are experiencing long COVID-19 symptoms.

Still, estimates on the numbers of people with long COVID are all over the map.

Researchers from the Penn State College of Medicine found that more than half of COVID-19 survivors had long COVID-19.

Another study from the University of Arizona found that about 2 out of 3 people who experienced mild or moderate cases of coronavirus had long-lasting symptoms.

Other reports have been more conservative, estimating anywhere between 10 to 30 percent of those infected develop long-term symptoms. Those who experience ongoing symptoms from long COVID-19 have sometimes come to be known as COVID-19 long haulers.

One problem in figuring out how many people get long COVID-19 is defining it.

Apart from the wide range of symptoms, there is still debate over when a person is considered to have long COVID-19. Some health care authorities consider a patient to have the condition if symptoms persist after three to six weeks, while other think it should be considered on a longer basis.

Jim Heath, president and professor at the Institute for Systems Biology, is leading the Pacific Northwest consortium researching long COVID-19 as part of the National Institute of Health's (NIH) RECOVER initiative, which is looking into the post-COVID-19 condition and potential ways of preventing and treating it.

Heath told The Hill that if one definition of long COVID-19 was being used — one in which symptoms lingered about four to six weeks after infection — then roughly half of those infected would be considered to have long COVID-19.

According to Heath, an estimate of 15 to 20 percent of coronavirus survivors experiencing long COVID-19 after six months was a reasonable "educated guess" and he added that there was evidence to support that rate of occurrence.

When reached for comment by The Hill, the NIH said initial studies have found that at least half of COVID-19 patients who were hospitalized reported "persistent weakness or fatigue" months after their recovery.

Studies on the prevalence of long COVID-19 have been "relatively few," according to the NIH, and they have all focused on people who had symptomatic cases of COVID-19.