Citing a dearth of knowledge about long Covid—including how common the condition is, what the risk factors are, how long it lasts, and how to treat it—some experts believe long Covid "is going to be the pandemic after the pandemic," Katherine Wu writes for The Atlantic.

Case study: Recovery clinics for Covid-19 long-haulers

How prevalent is long Covid?

Currently, most countries struggle to keep track of long Covid cases, so "many researchers have to make do with the limited data sets that are already available to them," Wu writes.

As a result, some studies are biased toward hospitalized patients, Wu writes, while others favor individuals who have the "time, means, and trust in the health care system" to participate in long-term studies. Unfortunately, neither group adequately captures the widespread toll of long Covid.

Ultimately, according to Erin Sanders, an NP and clinical scientist at Massachusetts Institute of Technology, the study of long Covid has become "a data disaster."

While some researchers estimate that a single-digit percentage of Covid-19 infections result in long Covid, others favor larger estimates—including some who insist that the rates are more than half. "Most of the experts I spoke with said they feel comfortable working in the 10% to 30% range, which is where many studies seem to be starting to converge," Wu writes.

Even if the proportion of Covid-19 infections that lead to long Covid is less than 10%—which is less than most expert estimates—in absolute terms "that is not small," said Ziyad Al-Aly, the director of the Clinical Epidemiology Center at the Veterans Affairs St. Louis Health Care System.

Millions of people have developed long Covid, and an unknown number have not fully recovered. For instance, the U.K.'s Office for National Statistics estimated that around 2% of U.K. residents—not just those with documented infections—might currently have long Covid. A separate analysis estimated that up to 23 million Americans have developed long Covid since the start of the pandemic.

Researchers still don't know enough about long Covid

In addition to limited information about the condition's prevalence, two years into the pandemic, researchers still do not know enough about long Covid as a condition.

For months, researchers have understood that long Covid is more of a category than a monolith. There are hundreds of possible symptoms associated with long Covid. It can impact an individual's brain, heart, lungs, gut, all of the above, or none of the above. Long Covid can begin with "a silent infection, an ICU-caliber case, or anything in between," Wu writes. Its onset can begin days, weeks, or months after a person's initial Covid-19 infection, and its severity can even fluctuate over time. 

Notably, Al-Aly roughly likens long Covid to cancer—an umbrella term for diseases that are related to each other but have their own distinct diagnoses and treatments. "We lump all of that into one broad thing," Al-Aly said. "It is not."

With the long list of potential symptoms, diagnosing long Covid—an essential step in understanding it—can be very difficult. "We don't have a clear-cut, consensus clinical definition, a single name for the condition, or a standardized set of tests to catch it," Wu writes.

In fact, even CDC and the World Health Organization don't agree on how long a person must be sick before they meet the criteria for long Covid.

As a result, some researchers and health care providers primarily follow one agency's definition, while others, dissatisfied with both definitions, create their own. In addition, "there are still doctors out there that do not think long Covid exists," said Alexandra Yonts, a pediatric infectious disease specialist at Children's National Hospital.

Formally dividing the disease into subdivisions could help address some of these ambiguities. However, we still don't know nearly enough to start "slicing and dicing," according to Bryan Lau, an infectious-disease epidemiologist.

Long Covid 'is going to be the pandemic after the pandemic'

While the public has been conditioned to believe that most Covid-19 infections have brief repercussions, "long Covid breaks the binary of severe and mild," Wu writes.

"It's going to continue to affect people, even people who are protected from severe illness during the acute phase of infection," said Michael Peluso, an infectious-disease physician and long-Covid researcher at University of California, San Francisco.

Ultimately, no matter where the numbers on long-Covid risk sit, they are too large to ignore. "Whether it's 10% or 50%, at both levels you have to do something about it," said Deepti Gurdasani, an epidemiologist at Queen Mary University of London.

"Statistics will help sharpen and clarify the condition's boundaries, and are still worth seeking out," Wu writes. "They will not, however, change long Covid's threat, at its core."

Although the global Covid-19 crisis can—in some ways—come to an end when the public decides to treat it like it is over, that is not an option for the growing number of long Covid patients who are unable to put Covid-19 fully behind them. "This is the challenge of chronic illness," Wu writes. "When people join its ranks, they do not always exit. With each new case of long Covid, the virus's burden balloons."

"This is going to be the pandemic after the pandemic," Gurdasani said. (Wu, The Atlantic, 3/11)