“Long haul” sufferers seemed like an aberration early in the COVID pandemic—an unfortunate few who, for whatever reason, couldn’t seem to kick the disease.

Nearly three years later, we know better. Long COVID is far from rare, and the ranks of those affected with it are swelling.

Up to one in five American adults who’ve had COVID-19 are living with long COVID, a condition loosely defined as symptoms that persist or appear long after the initial COVID infection is gone, according to the U.S. Centers for Disease Control and Prevention.

Many have accepted COVID infection as inevitable—and now even repeat COVID infection. It may be tempting to accept long COVID as inevitable too, especially given studies that have found that catching the virus multiple times may increase one’s risk of contracting it.

But such fatalistic thinking isn’t logical, Dr. Alexandra Brugler Yonts, an infectious disease specialist who runs a long COVID clinic at Children’s National Hospital in Washington, D.C., tells Fortune.

“That’s like saying every single person is going to get the flu,” she says. “Absolutes are dangerous.”

Dr. Panagis Galiatsatos, an assistant professor at Johns Hopkins’ Division of Pulmonary & Critical Care Medicine who treats long COVID patients, says that COVID doesn’t have a “binary outcome.”

“There’s a spectrum of how people get it,” he tells Fortune, adding that “how you catch COVID” may determine if you develop long COVID. For instance, those who vaccinate and/or treat their infection with antiviral Paxlovid may be at lower risk of developing the new disabling condition, some studies suggest.

Statistics like the CDC’s assertion that one in five U.S. adults who’ve had COVID have long COVID are generally based on surveys, with individuals self-identifying and not necessarily having been diagnosed.

Such surveys are basically asking, “Do you have any new health problems since you’ve had COVID?” Brugler Yonts says. “Which is a challenge, because life still goes on, and people still develop health conditions.”

It’s often impossible to say whether a post-COVID health condition would have occurred without an infection, or whether the infection hastened a disease process that was already occurring, she adds.

There’s no official consensus anyway on how to define the condition, which has more than 200 potential symptoms and can vary in onset from immediately after the infection resolves to months later.

“We’re still struggling as a medical entity to define long COVID appropriately,” Galiatsatos says. “There’s no biomarker, no test.”

These factors lead Galiatsatos and Brugler Yonts to believe that true long COVID is likely less common than we think—a reassuring thought.

All viruses are capable of causing complications after an infection is over, “and we need to tease those [cases] out,” Galiatsatos says.

“It’s no different than scraping your leg. The initial impact of the scrape is gone, but the scar will take time to heal. Patients who are still coughing at two months—that’s part of healing.”

COVID, like other viruses, can cause organ damage that “may take some time to improve,” he says.

But that isn’t long COVID, in his estimation. He defines true long COVID as new symptoms that persist six months or more after infection for which no other cause can be found. Such patients tend to have symptoms of breathlessness, chest discomfort, and fatigue, but no obvious organ damage, he says—and often had neurological symptoms, like headache and loss of taste and smell, during their acute infection.

“Long COVID is a diagnosis of exclusion,” Galiatsatos says. “There are many potential symptoms that are more incidental than anything else.”

Vaccination and antivirals like Paxlovid “may keep the viral load low enough to where it won’t develop into neurological complications,” Galiatsatos says. “It’s hard for me to believe that something this common is going to produce long COVID for everyone.”

Is long COVID is a personal inevitability or impossibility? It’s impossible to know, and such uncertainty can be demoralizing.

But don’t throw your hands in the air and caution to the wind, Brugler Yonts advises.

“Just because I’m probably going to get flu at another point in my life doesn’t mean I lick subway rails.”