E0 ConsensusPreliminaryPEM unclearReview-NarrativePeer-reviewedReviewed
Long COVID or Post-acute Sequelae of COVID-19 (PASC): An Overview of Biological Factors That May Contribute to Persistent Symptoms.
Proal, Amy D, VanElzakker, Michael B · Frontiers in microbiology · 2021 · DOI
Quick Summary
Some people who recover from COVID-19 infection continue to experience symptoms for months afterward, a condition called Long COVID or PASC. This review examines multiple biological explanations for why this happens, including organ damage, lingering virus in the body, reactivation of dormant viruses, immune system dysfunction, blood clotting problems, and the body's own immune cells attacking healthy tissues. The authors suggest that different patients likely have different underlying causes, which means different treatments may work best for different people.
Why It Matters
This work is significant for ME/CFS patients and researchers because it demonstrates that Long COVID shares multiple biological mechanisms with ME/CFS, suggesting that research and treatment strategies developed for one condition may inform understanding of the other. The emphasis on heterogeneous mechanisms validates the clinical observation that patients require individualized approaches, potentially accelerating more targeted therapeutic development.
Observed Findings
- Multiple biological mechanisms have been documented in acute COVID-19 and other virus-initiated syndromes that could contribute to persistent symptoms
- Epidemiological and experimental evidence suggests persistent viral reservoirs may occur in certain tissues
- Immune dysregulation patterns similar to ME/CFS have been observed in some PASC patients
- Coagulopathy and microbiome alterations have been documented in both acute COVID-19 and PASC
- Vagal/brainstem dysfunction has been proposed as a mechanism in both ME/CFS and PASC
Inferred Conclusions
- PASC likely results from multiple distinct biological pathways operating in different patient subsets rather than a single uniform mechanism
- The heterogeneity of PASC symptoms suggests that personalized diagnostic and therapeutic approaches targeting specific underlying mechanisms will be more effective than one-size-fits-all interventions
- ME/CFS research and PASC research should be integrated given significant mechanistic overlap between these conditions
Remaining Questions
- Which specific biological mechanisms predominate in which patient subpopulations, and can they be identified through biomarkers?
- How do these mechanisms interact, and do some mechanisms trigger others in a causal cascade?
What This Study Does Not Prove
This review does not prove that any single mechanism causes PASC or that all proposed mechanisms occur in all patients. It presents correlative evidence and plausible hypotheses rather than definitive causal relationships. The paper does not establish which mechanisms are most common or clinically significant in specific patient subpopulations.
Tags
Symptom:Post-Exertional MalaiseCognitive DysfunctionPainFatigue
Biomarker:CytokinesAutoantibodiesGene ExpressionBlood Biomarker
Phenotype:Infection-TriggeredLong COVID Overlap
Method Flag:Weak Case DefinitionExploratory Only
Metadata
- DOI
- 10.3389/fmicb.2021.698169
- PMID
- 34248921
- Review status
- Editor reviewed
- Evidence level
- Established evidence from major reviews, guidelines, or evidence maps
- Last updated
- 12 April 2026
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 →
Contribute
Private, reviewed by a human. Not a public comment thread.