Up to one in five American adults who’ve lived through COVID-19 are living with long COVID, according to the House Select Subcommittee on the Coronavirus Crisis, a condition defined by symptoms that persist or appear long after the initial COVID infection is gone. And an estimated 1 million Americans have been forced to leave the labor force because of medical complications from the nascent condition.

The congressional hearing, chaired by U.S. Rep. James Clyburn (D-S.C.), starts at 10 a.m and will be livestreamed. 

Among those testifying will be public health expert Dr. Monica Verduzco-Gutierrez, a professor at the University of Texas Health Science Center at San Antonio; economist Katie Bach, a nonresident senior fellow at Brookings Metro; and patient advocate Hannah Davis, cofounder of the Patient-Led Research Collaborative.

Verduzco-Gutierrez, a physiatrist, a doctor who specializes in physical medicine and rehabilitation, said in written testimony provided ahead of the hearing by the subcommittee that she has treated cancer patients who say long COVID is “100 times worse than their cancer fatigue ever was.”

“I have treated many nurses and physicians—some have not been able to return to the operating room or to the front line or the patient bedside,” she said. “Marathon runners who cannot even walk a mile. A young mother who can’t run after her children without her heart rate going to 180 and getting short of breath,” she wrote. 

Many patients, however, present with normal routine test results, making diagnosis and treatment—in addition to accessing disability benefits and insurance coverage—daunting, Verduzco-Gutierrez said.

“Patients may complain of shortness of breath, but show no discernible physical signs through imaging of their lungs,” she said. “A patient with brain fog who cannot find their words, or have head vibrations or dizziness, may have a normal MRI of their brain. The patient with fatigue 100 times worse than cancer fatigue will have all labs return normal.”

An estimated 28 million Americans have had long COVID at some point, though many have recovered. Around 16 million Americans are estimated to currently be suffering from long COVID, Bach said in written testimony provided by the subcommittee ahead of the hearing.

Of those, anywhere from 25% to 65% may have a reduced ability to work due to the condition, she said—around 2.4% of the U.S. employed population.

“This may sound unreasonably high, but it is not inconsistent with the experience of other comparable economies,” she said. 

A Bank of England representative recently said in a speech that labor force participation has dropped by around 1.3% for the population aged 16 to 64, not just those who are working, Bach said, adding that this is likely associated with long COVID.

While researchers are making strides in understanding what has become a common condition, long COVID is still poorly understood, and definitions vary.

The World Health Organization defines long COVID as a condition that occurs in someone who had COVID, with symptoms that cannot be explained by another diagnosis, that last for two months or more. The symptoms can persist following the initial onset, or come and go over time, the organization says, adding that a diagnosis of long COVID usually wouldn’t be made until three months after acute illness.

The Mayo Clinic defines long COVID as a set of symptoms stemming from COVID that persist for more than four weeks after diagnosis.

Whatever it is, studies have hypothesized that between 5% and 80% of those who’ve had COVID end up with long COVID, illustrating how poorly understood the condition is.

Common symptoms include fatigue, brain fog, and difficulty breathing, though hundreds of potential symptoms have been identified.

Long COVID is likely an umbrella term for a combination of issues and conditions: people who have long-term COVID infections who are able to continue to spread the disease; people whose COVID aftereffects clear up after a few weeks; and people with long COVID itself, in which people aren’t infectious but experience all kinds of symptoms for much longer. 

Muddying the waters, COVID patients whose disease was severe enough to require ICU admission may suffer post-ICU complications like muscle weakness, shortness of breath, cognitive issues, anxiety, and depression—symptoms that look a lot like long COVID but are not. Those issues might occur due to extended periods of immobility and ventilator use, and other traumatic medical events.