Long COVID may affect 1 in 6 infected patients

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Long COVID may be affecting far more Americans than current estimates suggest, with a study published last week in JAMA Network Open estimating that roughly one in six people infected with SARS-CoV-2 develop the condition, and nearly 90% go on to experience chronic health problems.

For the study, a team led by researchers at Massachusetts General Hospital analyzed health record data from 457,950 adults treated for COVID-19 (also known as postacute sequelae of SARS-CoV-2 infection, or PASC) across 58 hospitals and clinics in New England, Southeast Texas, Southern California, and Western Pennsylvania.

The researchers identified long COVID cases by detecting symptoms and conditions that emerged after infection and could not be explained by preexisting conditions.

15 million Americans may have long COVID

The team identified 74,560 long-COVID patients, representing 16.3% of COVID patients in the study. The estimate, which translates to roughly 15 million Americans, is far higher than the rate captured by current code-based surveillance systems. Prevalence ranged from 13.6% in Western Pennsylvania to 22.7% in Southern California.

Millions of people “would go entirely undetected by the diagnostic code that health systems and policymakers rely on to track the disease burden," senior author Hossein Estiri, PhD, of the Mass General Brigham (MGB) Department of Medicine, said in an MGB news release. "The figures we uncovered are almost certainly an undercount."

Long-COVID burden continues to grow

Most long-COVID patients (89.3%) identified in the study developed at least one chronic condition requiring ongoing clinical management.

The researchers also found evidence that the burden of long COVID continues to grow rather than fade. Long-COVID prevalence increased across all four studied regions through mid-2024.

Millions of people 'would go entirely undetected by the diagnostic code that health systems and policymakers rely on to track the disease burden.'

Hossein Estiri, PhD

“Our finding of persistently increasing cumulative prevalence through mid-2024 (4 years into the pandemic and well after widespread vaccination) contradicts assumptions that PASC represents a legacy of early, severe infection waves,” the authors write.

When the researchers used the quarterly increases they observed—which ranged from 0.3% to 1.5%—to estimate the relative increase in cumulative long-COVID prevalence over a decade, they found rates could increase 13% to 81%, “underscoring the substantial long-term burden if current trends persist.”

The study also revealed substantial differences in how long COVID manifests. Systemic, respiratory, and gastrointestinal symptoms were common across all regions, but endocrine complications varied in different parts of the country. New England patients were more likely to experience thyroid-related conditions, while patients in Texas, California, and Pennsylvania showed more metabolic abnormalities such as prediabetes and hyperglycemia.

Better surveillance, tailored treatments needed

Jiazi Tian, MSc, lead author and data scientist in the Clinical Augmented Intelligence Group at MGB, said many patients with long COVID are already receiving care but are not being recognized as having the condition.

"These patients are not absent from clinical care; they are absent from the diagnostic code that would identify them as long COVID patients," Tian said in the release. "The cardiologist seeing new dysautonomia, the endocrinologist seeing new metabolic disease, the neurologist seeing unexplained cognitive complaints—some of these presentations are long COVID arriving without the label that would connect them to a COVID-19 infection."

The findings suggest that long COVID has become a significant healthcare challenge, requiring better surveillance, coordinated care, and new treatments, argue the authors. They also conclude that because different people experience different combinations of symptoms, treatments should be individually tailored.