Transitional Changes in Fatigue-Related Symptoms Due to Long COVID: A Single-Center Retrospective Observational Study in Japan.
Nakano, Yasuhiro, Otsuka, Yuki, Honda, Hiroyuki et al. · Medicina (Kaunas, Lithuania) · 2022 · DOI
Quick Summary
This study compared long COVID symptoms in patients infected with different COVID-19 variants (Delta vs. Omicron) in Japan. Patients infected with Omicron had milder initial illness but were more likely to experience fatigue, sleep problems, and ongoing cough. Those infected with Delta were more likely to lose their sense of taste or smell and experience hair loss.
Why It Matters
Understanding how different COVID-19 variants produce distinct long-term symptom patterns helps clinicians recognize and manage post-COVID conditions more effectively. For ME/CFS researchers, this study provides evidence that fatigue-predominant presentations may be variant-dependent, which could inform investigation of biological mechanisms driving persistent fatigue and post-exertional malaise in long COVID.
Observed Findings
Omicron-infected patients had significantly higher fatigue frequency (65% vs. 50%, p<0.05) compared to Delta-infected patients
Omicron-infected patients had significantly higher insomnia frequency (26% vs. 13%, p<0.05) compared to Delta-infected patients
Omicron-infected patients had significantly lower loss of smell/taste (12% vs. 45%, p<0.01) and lower hair loss (7% vs. 28%, p<0.01)
Omicron-infected patients had fewer hospitalizations and visited the aftercare clinic earlier than Delta-infected patients
Omicron-infected patients had higher vaccination rates than Delta-infected patients
Inferred Conclusions
Viral variants produce distinct phenotypes in long COVID symptom presentation, with Omicron-infection associated with fatigue and sleep disturbance dominance
Milder acute COVID-19 illness (as seen with Omicron) does not protect against chronic fatigue and insomnia symptoms
Sensory symptoms (taste/smell loss) and hair loss may be more variant-specific or acute illness-severity dependent than fatigue symptoms
Do the observed symptom differences persist at longer follow-up intervals, or do symptom profiles converge over time?
What This Study Does Not Prove
This study does not prove that viral variants directly cause specific symptom patterns—hospitalization rates and vaccination status also differed between groups and could contribute to symptom differences. Correlation between variant type and symptom presentation does not establish the biological mechanisms responsible. The retrospective design and single Japanese center limit generalizability to other populations.
Tags
Symptom:Unrefreshing SleepFatigue
Phenotype:Infection-TriggeredLong COVID Overlap
Method Flag:PEM Not DefinedWeak Case DefinitionNo ControlsMixed Cohort