Understanding Long COVID: The Impact of Varying Definitions on Prevalence Estimates

Long COVID, also known as post-acute sequelae of SARS-CoV-2 infection, remains an area of active research and debate within the medical community. Despite numerous studies and millions of affected individuals worldwide, there is still no universally accepted definition of the condition. This lack of standardization significantly complicates efforts to accurately diagnose, treat, and understand long COVID.

Recent research from UCLA highlights the extent of this issue, demonstrating that different definitions used across studies can lead to vastly different estimates of how many people experience long COVID. The study, published in August 2025 in JAMA Network Open, assessed five prevalent definitions from studies conducted in various countries, including the US, UK, Netherlands, Sweden, and Puerto Rico. These definitions varied in terms of symptom duration, ranging from just 4 weeks to six months, and in the number of symptoms considered, from nine to forty-four. Applying these definitions to a cohort of 4,700 US patients from the INSPIRE study revealed that the estimated prevalence of long COVID ranged widely from 15% to 42%, despite examining the same population.

Moreover, the analysis showed that published definitions had only moderate sensitivity in correctly identifying individuals with long COVID compared to patients’ own reports of their symptoms. While some definitions performed better in specificity, none achieved an ideal level for clinical or research purposes. This inconsistency hampers the ability to compare studies accurately, develop effective treatments, and track the progress of the condition across different populations.

The study's senior author, Dr. Joann Elmore, emphasized the importance of establishing a standard definition. In the absence of an objective diagnostic test like a blood test, and with varied criteria, clinicians and researchers face challenges in accurately diagnosing long COVID. This variability can lead to either missing some genuine cases or mislabeling patients who do not actually have long COVID, ultimately impacting patient care and scientific progress.

In conclusion, the research underscores the urgent need for a standardized, clinically applicable definition of long COVID. Such a standard would improve comparability across studies, facilitate better understanding, and aid in the development of targeted treatments. Until then, healthcare providers must carefully consider the definitions they use and acknowledge their limitations when diagnosing and managing long COVID.

Source: https://medicalxpress.com/news/2025-08-covid-definitions-widely-varying.html