Long COVID—like so many invisible illnesses—is far more impactful than many healthy individuals realize.

A new study out of the U.K. reveals the extreme extent of its debilitating nature, with thousands of patients reporting more trouble functioning, greater fatigue, and lower quality of life than those with serious and even life-threatening medical conditions like advanced cancer, Parkinson’s disease, and end-stage kidney disease.

Researchers at University College London (UCL) and the University of Exeter surveyed nearly 4,000 U.K. adults who had been referred to long-COVID clinics. They found that functional impairment—affecting their ability to work, keep up their homes, and enjoy leisure activities—was generally worse among such patients than it was in those who had experienced a stroke, and was similar to that of Parkinson’s disease patients.

Half of patients reported missing work one or more days the previous month because of symptoms, and a fifth reported missing between three and four weeks of work during the previous month.

Study participants also reported dismally low health-related quality of life, with scores similar to those of patients with advanced cancer. Quality of life is generally better among stage 4 lung cancer patients than it is among long-COVID patients, the authors wrote.

The driving factor behind functional impairment and low quality of life is fatigue, which is generally worse than that experienced by those who have end-stage kidney disease or both cancer and anemia. Other symptoms that impact quality of life include breathlessness, anxiety, depression, and brain fog, researchers reported.

While up to 17% of COVID patients go on to develop the post-viral illness, long COVID is still poorly understood, Dr. Henry Goodfellow, a general practitioner, professor at UCL, and lead author of the study, said in a news release.

“Our results have found that long COVID can have a devastating effect on the lives of patients, with fatigue having the biggest impact on everything from social activities to work, chores, and maintaining close relationships,” he said.

William Henley, a professor of medical statistics at the University of Exeter and another author of the study, noted that while long COVID can leave people more fatigued and with worse quality of life than those with some cancers, “support and understanding is not at the same level.”

“We urgently need more research to enable the development of evidence-based services to support people trying to manage this debilitating new condition,” he said.

Symptoms of long COVID

While definitions of long COVID—or post-acute sequelae of COVID (PASC)—vary, it’s generally defined as new symptoms that occur with COVID infection, or develop shortly thereafter, and last for 12 or more weeks.

True long COVID, many experts say, is best defined as a chronic fatigue syndrome–like condition that develops after a COVID infection, similar to other post-viral syndromes that can occur after an infection with herpes, Lyme disease, and Ebola, among others.

Other post-COVID complications like organ damage and post–intensive care syndrome—experienced by patients with traumatic hospital stays that include intubation and prolonged bed confinement—should not be considered long COVID, they contend.

The trouble for patients and clinicians alike is the vast array of other symptoms that can occur with the condition. More than 200 have been identified, from lingering cough and ear numbness to a sensation of “brain on fire” and new erectile dysfunction.

Those with long COVID experienced an average of 60 symptoms in nine different organ systems over nine or more months before recovering, if symptoms ever subsided, according to a landmark study published last summer in The Lancet.