The fatigue spectrum in a community-based long haul COVID cohort.
Carter, Isabelle V, May, Anna, Hsieh, Isabella C et al. · Sleep & breathing = Schlaf & Atmung · 2026 · DOI
Quick Summary
This study looked at 277 people with long COVID who visited a specialized clinic, focusing on those experiencing fatigue. About 73% reported fatigue as a main symptom, but only about 22% of those met the strict ME/CFS diagnostic criteria. The researchers found that fatigue severity varied widely, and fatigue often came alongside other symptoms like brain fog, anxiety, and reduced physical functioning.
Why It Matters
This study demonstrates that post-COVID fatigue presents as a heterogeneous spectrum rather than a single condition, with only about 1 in 5 fatigued patients meeting ME/CFS criteria. Understanding this diversity is crucial for researchers designing clinical trials and for clinicians tailoring treatment approaches to individual patients rather than applying one-size-fits-all protocols.
Observed Findings
73.5% of long COVID clinic patients presented with fatigue as a primary or co-primary complaint
21.9% of fatigued patients met full 2015 CDC ME/CFS diagnostic criteria; 78.1% did not
Fatigue Severity Score was significantly higher in those with primary fatigue complaints (5.31 vs. 4.43, p<0.001)
Anxiety was present in 58% of fatigued patients versus 38% of non-fatigued patients (p<0.02)
Brain fog occurred in approximately 52% of patients and correlated independently with FSS>4, functional impairment, and depression
Inferred Conclusions
Post-COVID fatigue exists on a spectrum with heterogeneous presentations; formal ME/CFS criteria apply to only a minority of fatigued long COVID patients
Associated psychiatric symptoms, particularly anxiety, and functional impairment are key features of the fatigue phenotype
Brain fog operates as a distinguishing symptom with separate clinical correlates from fatigue alone
The heterogeneity of post-COVID fatigue phenotypes will complicate the design and interpretation of clinical trials using standard diagnostic criteria
Remaining Questions
What mechanisms distinguish the 22% meeting ME/CFS criteria from the 78% with fatigue not meeting criteria?
What This Study Does Not Prove
This study does not establish causality between COVID-19 and fatigue spectrum presentations, nor does it determine whether post-COVID fatigue is mechanistically distinct from ME/CFS or other fatigue disorders. The referral clinic sample may not represent the broader long COVID population, potentially overrepresenting more severe cases. Cross-sectional design prevents determination of whether psychiatric symptoms precede or follow fatigue onset.
Does the proportion of patients meeting ME/CFS criteria change at different time points post-infection, and is there a natural trajectory?
Are pre-COVID factors (prior psychiatric history, sleep conditions) predictive of which fatigued long COVID patients develop ME/CFS-meeting presentations?
What are the optimal diagnostic and treatment approaches for the larger subgroup with post-COVID fatigue that does not meet ME/CFS criteria?