The scope of long COVID is bigger than we think, Mass. researchers say

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Six years since the start of the COVID-19 pandemic, millions of Americans have suffered long-term symptoms of the virus.

But exactly how many people developed long COVID — defined as when symptoms last at least three months — is hard to pin down. Scientists are still trying to understand how the disease works, and doctors don’t always know how to recognize it.

Long COVID can be elusive because it causes a range of different symptoms: fatigue, difficulty breathing, joint pain, heart palpitations, dizziness, depression, menstrual changes and more.

New research from Mass General Brigham suggests that at least 10 million Americans have long COVID — but have not been diagnosed. To arrive at these findings, the researchers used artificial intelligence to draw a fuller picture of the lasting effects of the COVID virus.

“We built an AI to map the post-pandemic reality, and it uncovered a 10 million-person blind spot in the American healthcare system,” said Hossein Estiri, an author of the study and leader of MGB’s clinical augmented intelligence research group.

Estiri’s team, with the artificial intelligence tool, analyzed nearly 460,000 medical records of patients across the country. The researchers tracked how many patients tested positive for COVID, and later sought care for health problems linked to long COVID. Their study suggests 16% of people who get COVID develop long-term symptoms, but those symptoms are not always identified as long COVID.

“If someone has fatigue, it doesn't really matter at the moment whether it's a COVID-induced fatigue — the doctor just tries to treat the fatigue,” Estiri said. “It's really hard to connect the dots back to the roots. This is not how the healthcare system in general is designed to work.”

While COVID is no longer spreading in big waves, it is still making people chronically ill, he added.

“The burden of these new chronic diseases is accumulating,” he said.“It is a compounding crisis.”

Estiri’s count of long COVID patients, published last week in the medical journal JAMA Network Open, is more than twice as high as some previous estimates. The World Health Organization, for example, estimates 6% of COVID patients develop chronic symptoms.

But according to a 2024 report from the federal Centers for Disease Control and Prevention, 18% of U.S. adults surveyed said they had experienced long COVID.

Dr. Ziyad Al-Aly, a long COVID expert and professor of medicine at Washington University in St. Louis, said Estiri’s study does not control for important variables and therefore overstates the problem of long COVID.

“I think Long Covid is a serious national and global problem that demands attention from governments and international bodies,” he said by email. “I don't think the data in this paper helps.”

Other researchers said the results seem plausible.

“ I think it shows that long COVID is a persistent illness,” said Beth Pollack, a research scientist at Massachusetts Institute of Technology who studies long COVID and other chronic illnesses. “I think sometimes there can be a misconception that people can get sick with long COVID and they'll just get better. And for many patients, that is not true. And it can be an incredibly disabling, multi-system illness that deeply impacts quality of life.”

Dr. Sandeep Jubbal, an infectious disease specialist at UMass Memorial Health, said he still treats new patients seeking care for long COVID, and some whose symptoms have lingered for years.

There is no single test doctors can use to diagnose long COVID, or to determine if a patient recovers.

“Not having a diagnostic test is a big limitation,” Jubbal said. “Most of the diagnosis is symptom-based.”

Beth Stelson, a  social epidemiologist who studies long COVID, said the condition is one of a few — including chronic Lyme disease and chronic fatigue syndrome — that are often missed because they’re poorly understood. These conditions start with a bacterial or viral infection, then develop into chronic problems that can last for years. There are no known cures.

Previous research indicates that people at higher risk of long COVID include women, people with underlying health conditions, and people who did not receive a COVID vaccine. Studies of long COVID are ongoing.

Patients with long COVID sometimes get misdiagnosed with mental health conditions, said Stelson, an associate professor at Washington University.

“While we've come miles in recognizing that long COVID is a medical disorder,” she said, “there is still some psychologizing that happens with the illness. It can be dismissed as anxiety.”

Stelson is a member of the Patient-Led Research Collaborative, a group of researchers who have chronic conditions such as long COVID. Like many patients, Stelson said, she’s had to limit her work and physical activity because of severe exhaustion, known as post-exertional malaise. Over the six years since she developed long COVID, her symptoms have sometimes improved, sometimes worsened.

“I am not completely better,” Stelson said. “I think that is one of the challenging things about this disease is the ebb and flow, the relapsing.”