Peter, Raphael S, Nieters, Alexandra, Göpel, Siri et al. · PLoS medicine · 2025 · DOI
This study followed nearly 1,000 people who had long-term COVID symptoms for over a year to see who improved and who stayed sick. Researchers found that about two-thirds of patients still had symptoms in the second year after infection, with fatigue, breathing problems, and thinking difficulties being the most common complaints. People who got better tended to have had milder initial infections and were more educated, while those who stayed sick were more likely to be overweight and have had specialist medical care or rehabilitation.
This study provides crucial population-based evidence that post-COVID syndrome frequently persists into the second year in working-age adults, with objective evidence of reduced exercise capacity and cognitive dysfunction despite normal laboratory results. For ME/CFS research, the identification of post-exertional malaise (PEM) as a marker of greater disease severity aligns with ME/CFS diagnostic criteria and suggests PEM may be valuable for stratifying patient severity across post-viral conditions. The finding that standard medical investigations fail to identify pathology in persistent cases highlights the urgent need for novel biomarkers and mechanistic research in post-viral illnesses.
This study does not establish causality for the observed associations with PCS persistence (e.g., obesity, educational status, smoking) and cannot determine whether these are risk factors, consequences of illness, or confounders. The study cannot prove that the cognitive deficits or reduced exercise capacity existed before COVID infection, as there were no pre-infection baseline measurements, making pre-existing illness a potential confounder. The negative viral persistence and EBV reactivation findings do not exclude other potential mechanisms (mitochondrial dysfunction, autonomic dysfunction, microclotting, or other pathophysiology) in PCS/ME-CFS pathogenesis.
About the PEM badge: “PEM required” means post-exertional malaise was an explicit required diagnostic criterion for participant inclusion in this study — not that PEM was studied, observed, or discussed. Studies using criteria that do not require PEM (e.g. Fukuda, Oxford) are tagged “PEM not required”. How the atlas works →
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