Morita, Satoru, Tokumasu, Kazuki, Otsuka, Yuki et al. · PloS one · 2024 · DOI
This study looked at 739 patients with long COVID to understand how many developed ME/CFS and what factors were involved. Researchers found that ME/CFS affected about 8% of long COVID patients, but the rate varied depending on which COVID variant caused the initial infection—it was much higher (24%) in early COVID but dropped significantly (3%) during the Omicron wave. Brain fog complaints increased over time, even as strict ME/CFS diagnoses became less common.
Understanding variant-dependent patterns in long COVID-related ME/CFS is crucial for clinicians to recognize and diagnose the condition accurately, particularly as dominant variants change. This research highlights that subjective symptoms like brain fog may persist or even increase even when formal ME/CFS criteria are met less frequently, suggesting evolving phenotypes that warrant continued clinical attention and research.
This study does not prove that COVID variants cause ME/CFS through different mechanisms, nor does it establish causation for the identified risk factors (smoking, alcohol, vaccination status). The retrospective design cannot eliminate confounding from changes in diagnostic awareness, variant-specific disease biology, or population differences over the study period. Cross-sectional data cannot track individual symptom progression or recovery patterns.
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 →
The first block is for the primary paper and is the citation you should use in research work. The atlas-snapshot line only applies if you are specifically referring to this atlas’s reading of the paper on the date shown.
Primary citation
Morita, Satoru, Tokumasu, Kazuki, Otsuka, Yuki, Honda, Hiroyuki, Nakano, Yasuhiro, Sunada, Naruhiko, et al. (2024). Phase-dependent trends in the prevalence of myalgic encephalomyelitis / chronic fatigue syndrome (ME/CFS) related to long COVID: A criteria-based retrospective study in Japan.. PloS one. https://doi.org/10.1371/journal.pone.0315385
BibTeX
@article{mecfsatlas-morita-2024-phase-dependent,
author = {Morita, Satoru and Tokumasu, Kazuki and Otsuka, Yuki and Honda, Hiroyuki and Nakano, Yasuhiro and Sunada, Naruhiko and Sakurada, Yasue and Matsuda, Yui and Soejima, Yoshiaki and Ueda, Keigo and Otsuka, Fumio},
title = {Phase-dependent trends in the prevalence of myalgic encephalomyelitis / chronic fatigue syndrome (ME/CFS) related to long COVID: A criteria-based retrospective study in Japan.},
journal = {PloS one},
year = {2024},
doi = {10.1371/journal.pone.0315385},
note = {PubMed: 39652555},
url = {https://www.mecfsatlas.com/evidence/morita-2024-phase-dependent},
}Atlas snapshot reference
ME/CFS Atlas. Generator v1 / Scanner v1.4 / policy v0.1. Accessed 2026-05-29. https://www.mecfsatlas.com/evidence/morita-2024-phase-dependent
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