Scientists Discover a “Hidden Epidemic” After COVID-19

A new study suggests that the true scale of long COVID may be significantly underestimated. According to research published in JAMA Network Open, approximately 16% of people who had COVID-19 develop long-term symptoms — equivalent to more than 18 million people in the United States, nearly double previous estimates.

The study was conducted by a team from Mass General Brigham in Boston, led by Hossein Estiri. Researchers say current diagnostic systems identify fewer than 7% of cases, meaning that a large proportion of patients are effectively “missing” from official medical statistics.

To gain a more accurate picture, the scientists developed an artificial intelligence algorithm that analyzed medical records and identified signs of long COVID based on the appearance of new diseases and symptoms after infection that could not be explained by patients’ previous medical history.

The model was applied to data from nearly 460,000 patients across 58 hospitals in the United States. The results showed that:
• around 16% of patients had signs of long COVID;
• rates varied from approximately 14% to nearly 23% across different regions;
• the number of cases continued to rise through mid-2024.

Researchers also found that long COVID is not simply a “legacy” of the early pandemic waves, as previously believed. On the contrary, new cases continue to emerge, and some regions are even seeing increasing numbers.

According to the researchers, the real number of patients may be even higher because many cases are not captured in official statistics due to the absence of proper diagnostic coding.

One major challenge is that patients with long COVID often visit different specialists with different symptoms: cardiologists detect autonomic nervous system disorders, endocrinologists observe metabolic dysfunction, while neurologists identify cognitive impairments. However, these symptoms are frequently not connected to one another or linked back to the original infection.

The authors emphasize that the lack of a unified diagnostic “label” prevents healthcare systems from understanding the true scale of the problem and providing timely care to patients.

If current trends continue, researchers warn that the number of long COVID cases could continue rising over the next decade.

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