Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: the biology of a neglected disease

Cerebrospinal fluid immune phenotyping reveals distinct immunotypes of myalgic encephalomyelitis/chronic fatigue syndrome

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a complex heterogeneous multiorgan disease that can have severe impact on individuals' quality of life. Diagnosis of ME/CFS is based on symptom presentation, and a significant goal for the field is to establish meaningful subtypes. The heterogeneity in the literature suggests that individuals living with ME/CFS may suffer from overlapping but different underlying pathophysiological mechanisms. We enrolled 40 participants with ME/CFS and 41 matched healthy control subjects at the Bragée Clinic in Sweden. We assessed plasma samples from both ME/CFS cases and control groups and cerebrospinal fluid (CSF) samples from individuals with ME/CFS. We investigated dysregulated pathways and disease profiles through clinical questionnaires; multiplex analyses of cytokines, hormones, and matrix metalloproteinases; pathogen seroreactivity through peptide display bacteria libraries; and high-throughput microarray for autoantibodies. All samples used were from humans. We show altered interaction patterns between circulating biological factors in plasma of ME/CFS participants. Our analysis of CSF from individuals with ME/CFS revealed different immunotypes of disease. We found 2 patient clusters based on matrix metalloproteinases profiles. The subgroups had similar clinical presentation but distinct pathogen exposure and CSF inflammatory profiles. Our findings shed light on ME/CFS immune phenotypes and generate hypotheses for future research in disease pathogenesis and treatment development by exploring disease subgroups.

A Direct Relationship Between 'Blood Stasis' and Fibrinaloid Microclots in Chronic, Inflammatory, and Vascular Diseases, and Some Traditional Natural Products Approaches to Treatment

'Blood stasis' (syndrome) (BSS) is a fundamental concept in Traditional Chinese Medicine (TCM), where it is known as Xue Yu (). Similar concepts exist in Traditional Korean Medicine ('Eohyul') and in Japanese Kampo medicine (Oketsu). Blood stasis is considered to underpin a large variety of inflammatory diseases, though an exact equivalent in Western systems medicine is yet to be described. Some time ago we discovered that blood can clot into an anomalous amyloid form, creating what we have referred to as fibrinaloid microclots. These microclots occur in a great many chronic, inflammatory diseases are comparatively resistant to fibrinolysis, and thus have the ability to block microcapillaries and hence lower oxygen transfer to tissues, with multiple pathological consequences. We here develop the idea that it is precisely the fibrinaloid microclots that relate to, and are largely mechanistically responsible for, the traditional concept of blood stasis (a term also used by Virchow). First, the diseases known to be associated with microclots are all associated with blood stasis. Secondly, by blocking red blood cell transport, fibrinaloid microclots provide a simple mechanistic explanation for the physical slowing down ('stasis') of blood flow. Thirdly, Chinese herbal medicine formulae proposed to treat these diseases, especially Xue Fu Zhu Yu and its derivatives, are known mechanistically to be anticoagulatory and anti-inflammatory, consistent with the idea that they are actually helping to lower the levels of fibrinaloid microclots, plausibly in part by blocking catalysis of the polymerization of fibrinogen into an amyloid form. We rehearse some of the known actions of the constituent herbs of Xue Fu Zhu Yu and specific bioactive molecules that they contain. Consequently, such herbal formulations (and some of their components), which are comparatively little known to Western science and medicine, would seem to offer the opportunity to provide novel, safe, and useful treatments for chronic inflammatory diseases that display fibrinaloid microclots, including Myalgic Encephalopathy/Chronic Fatigue Syndrome, long COVID, and even ischemic stroke.

The potential therapeutic approaches targeting gut health in myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS): a narrative review

BACKGROUND

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is a complex disorder characterized by persistent fatigue and cognitive impairments, with emerging evidence highlighting the role of gut health in its pathophysiology. The main objective of this review was to synthesize qualitative and quantitative data from research examining the gut microbiota composition, inflammatory markers, and therapeutic outcomes of interventions targeting the microbiome in the context of ME/CFS.

METHODS

The data collection involved a detailed search of peer-reviewed English literature from January 1995 to January 2025, focusing on studies related to the microbiome and ME/CFS. This comprehensive search utilized databases such as PubMed, Scopus, and Web of Science, with keywords including "ME/CFS," "Gut-Brain Axis," "Gut Health," "Intestinal Dysbiosis," "Microbiome Dysbiosis," "Pathophysiology," and "Therapeutic Approaches." Where possible, insights from clinical trials and observational studies were included to enrich the findings. A narrative synthesis method was also employed to effectively organize and present these findings.

RESULTS

The study found notable changes in the gut microbiota diversity and composition in ME/CFS patients, contributing to systemic inflammation and worsening cognitive and physical impairments. As a result, various microbiome interventions like probiotics, prebiotics, specific diets, supplements, fecal microbiota transplantation, pharmacological interventions, improved sleep, and moderate exercise training are potential therapeutic strategies that merit further exploration.

CONCLUSIONS

Interventions focusing on the gut-brain axis may help reduce neuropsychiatric symptoms in ME/CFS by utilizing the benefits of the microbiome. Therefore, identifying beneficial microbiome elements and incorporating their assessments into clinical practice can enhance patient care through personalized treatments. Due to the complexity of ME/CFS, which involves genetic, environmental, and microbial factors, a multidisciplinary approach is also necessary. Since current research lacks comprehensive insights into how gut health might aid ME/CFS treatment, standardized diagnostics and longitudinal studies could foster innovative therapies, potentially improving quality of life and symptom management for those affected.

Dissecting the genetic complexity of myalgic encephalomyelitis/chronic fatigue syndrome via deep learning-powered genome analysis

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a complex, heterogeneous, and systemic disease defined by a suite of symptoms, including unexplained persistent fatigue, post-exertional malaise (PEM), cognitive impairment, myalgia, orthostatic intolerance, and unrefreshing sleep. The disease mechanism of ME/CFS is unknown, with no effective curative treatments. In this study, we present a multi-site ME/CFS whole-genome analysis, which is powered by a novel deep learning framework, HEAL2. We show that HEAL2 not only has predictive value for ME/CFS based on personal rare variants, but also links genetic risk to various ME/CFS-associated symptoms. Model interpretation of HEAL2 identifies 115 ME/CFS-risk genes that exhibit significant intolerance to loss-of-function (LoF) mutations. Transcriptome and network analyses highlight the functional importance of these genes across a wide range of tissues and cell types, including the central nervous system (CNS) and immune cells. Patient-derived multi-omics data implicate reduced expression of ME/CFS risk genes within ME/CFS patients, including in the plasma proteome, and the transcriptomes of B and T cells, especially cytotoxic CD4 T cells, supporting their disease relevance. Pan-phenotype analysis of ME/CFS genes further reveals the genetic correlation between ME/CFS and other complex diseases and traits, including depression and long COVID-19. Overall, HEAL2 provides a candidate genetic-based diagnostic tool for ME/CFS, and our findings contribute to a comprehensive understanding of the genetic, molecular, and cellular basis of ME/CFS, yielding novel insights into therapeutic targets. Our deep learning model also offers a potent, broadly applicable framework for parallel rare variant analysis and genetic prediction for other complex diseases and traits.

Unequal access to diagnosis of myalgic encephalomyelitis in England

BACKGROUND

People with Myalgic Encephalomyelitis (ME/CFS; sometimes referred to as chronic fatigue syndrome) experience poor health-related quality of life and only rarely recover. ME/CFS has no curative treatment, and no single diagnostic test. Public health and policy decisions relevant to ME/CFS require knowledge of its prevalence and barriers to diagnosis. However, people with ME/CFS report lengthy diagnostic delays and prevalence estimates vary greatly due to uneven diagnosis and misdiagnosis. Factors that influence diagnosis could be revealed by stratifying a single population by gender, age and ethnicity.

METHODS

Hospital Episode Statistics data, routinely collected by the NHS in England, was downloaded from the Feasibility Self-Service of NHS DigiTrials. This was used to stratify individuals with the ICD-10 code that best reflects ME/CFS symptoms (G93.3) according to age, self-reported gender and ethnicity, General Practice and NHS England Integrated Care Board (ICB).

RESULTS

In all, 100,055 people in England had been diagnosed with ME/CFS (ICD-10:G93.3) between April 1 1989 and October 7 2023, 0.16% of all registered patients. Of these, 79,445 were females and 20,590 males, a female-to-male ratio of 3.88:1. Female relative to male prevalence peaked at about 6-to-1 in individuals' fourth and fifth decades of life. Prevalence varied widely across the 42 ICBs: 0.086%-0.82% for females and 0.024%-0.21% for males. White individuals were approximately fivefold more likely to be diagnosed with ME/CFS than others; Black, Asian or Chinese ethnicities are associated with particularly low rates of ME/CFS diagnoses. This ethnicity bias is stronger than for other common diseases. Among active English GP practices, 176 (3%) had no registered ME/CFS patients. Eight ICBs (19%) each contained fewer than 8 other-than-white individuals with a G93.3 code despite their registers containing a total of 293,770 other-than-white patients.

CONCLUSION

Other-than-white ethnic groups, older females (> 60y), older males (> 80y), and people living in areas of multiple deprivation are disproportionately undiagnosed with ME/CFS. Lifetime prevalence of ME/CFS for English females and males may be as high as 0.92% and 0.25%, respectively, or approximately 404,000 UK individuals overall (0.6%). This improved estimate of ME/CFS prevalence allows more accurate assessment of the socioeconomic and disease burden imposed by ME/CFS.

Immunological Avalanches in Renal Immune Diseases

The complex nature of immune system behavior in both autoimmune diseases and transplant rejection can be understood through the lens of avalanche dynamics in critical-point systems. This paper introduces the concept of the "immunological avalanche" as a framework for understanding unpredictable patterns of immune activity in both contexts. Just as avalanches represent sudden releases of accumulated potential energy, immune responses exhibit periods of apparent stability followed by explosive flares triggered by seemingly minor stimuli. The model presented here draws parallels between immune system behavior and other complex systems such as earthquakes, forest fires, and neuronal activity, where localized events can propagate into large-scale disruptions. In autoimmune conditions like systemic lupus erythematosus (SLE), which affects multiple organ systems including the kidneys in approximately 50% of patients, these dynamics manifest as alternating periods of remission and flares. Similarly, in transplant recipients, the immune system exhibits metastable behavior under constant allograft stimulation. This critical-point dynamics framework is characterized by threshold-dependent activation, positive feedback loops, and dynamic non-linearity. In autoimmune diseases, triggers such as UV light exposure, infections, or stress can initiate cascading immune responses. In transplant patients, longitudinal analysis reveals how monitoring oscillatory patterns in blood parameters and biological age markers can predict rejection risk. In a preliminary study on kidney transplant, all measured variables showed temporal instability. Proteinuria exhibited precise log-log linearity in power law analysis, confirming near-critical-point system behavior. Two distinct dynamic patterns emerged: large oscillations in eGFR, proteinuria, or biological age predicted declining function, while small oscillations indicated stability. During avalanche events, biological age increased dramatically, with partial reversal leaving persistent elevation after acute episodes. Understanding these dynamics has important implications for therapeutic approaches in both contexts. Key findings suggest that monitoring parameter oscillations, rather than absolute values, better indicates system instability and potential avalanche events. Additionally, biological age calculations provide valuable prognostic information, while proteinuria measurements offer efficient sampling for system dynamics assessment. This conceptual model provides a unifying framework for understanding the pathogenesis of both autoimmune and transplant-related immune responses, potentially leading to new perspectives in disease management and rejection prediction.

The effect of biocide chloromethylisothiazolinone/methylisothiazolinone (CMIT/MIT) mixture on C2C12 muscle cell damage attributed to mitochondrial reactive oxygen species overproduction and autophagy activation

The mixture of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one (CMIT/MIT) is a biocide widely used as a preservative in various commercial products. This biocide has also been used as an active ingredient in humidifier disinfectants in South Korea, resulting in serious health effects among users. Recent evidence suggests that the underlying mechanism of CMIT/MIT-initiated toxicity might be associated with defects in mitochondrial functions. The aim of this study was to utilize the C2C12 skeletal muscle model to investigate the effects of CMIT/MIT on mitochondrial function and relevant molecular pathways associated with skeletal muscle dysfunction. Data demonstrated that exposure to CMIT/MIT during myogenic differentiation induced significant mitochondrial excess production of reactive oxygen species (ROS) and a decrease in intracellular ATP levels. Notably, CMIT/MIT significantly inhibited mitochondrial oxidative phosphorylation (Oxphos) and reduced mitochondrial mass at a lower concentration than the biocide amount, which diminished the viability of myotubes. CMIT/MIT induced activation of autophagy flux and decreased protein expression levels of myosin heavy chain (MHC). Taken together, CMIT/MIT exposure produced damage in C2C12 myotubes by impairing mitochondrial bioenergetics and activating autophagy. Our findings contribute to an increased understanding of the underlying mechanisms associated with CMIT/MIT-induced adverse skeletal muscle health effects.

Exploring the shared mechanism of fatigue between systemic lupus erythematosus and myalgic encephalomyelitis/chronic fatigue syndrome: monocytic dysregulation and drug repurposing

Background

SLE and ME/CFS both present significant fatigue and share immune dysregulation. The mechanisms underlying fatigue in these disorders remain unclear, and there are no standardized treatments. This study aims to explore shared mechanisms and predict potential therapeutic drugs for fatigue in SLE and ME/CFS.

Methods

Genes associated with SLE and ME/CFS were collected from disease target and clinical sample databases to identify overlapping genes. Bioinformatics analyses, including GO, KEGG, PPI network construction, and key target identification, were performed. ROC curve and correlation analysis of key targets, along with single-cell clustering, were conducted to validate their expression in different cell types. Additionally, an inflammation model was established using THP-1 cells to simulate monocyte activation in both diseases in vitro, and RT-qPCR was used to validate the expression of the key targets. A TF-mRNA-miRNA co-regulatory network was constructed, followed by drug prediction and molecular docking.

Results

Fifty-eight overlapping genes were identified, mainly involved in innate immunity and inflammation. Five key targets were identified (IL1β, CCL2, TLR2, STAT1, IFIH1). Single-cell sequencing revealed that monocytes are enriched with these targets. RT-qPCR confirmed significant upregulation of these targets in the model group. A co-regulatory network was constructed, and ten potential drugs, including suloctidil, N-Acetyl-L-cysteine, simvastatin, ACMC-20mvek, and camptothecin, were predicted. Simvastatin and camptothecin showed high affinity for the key targets.

Conclusion

SLE and ME/CFS share immune and inflammatory pathways. The identified key targets are predominantly enriched in monocytes at the single-cell level, suggesting that classical monocytes may be crucial in linking inflammation and fatigue. RT-qPCR confirmed upregulation in activated monocytes. The TF-mRNA-miRNA network provides a foundation for future research, and drug prediction suggests N-Acetyl-L-cysteine and camptothecin as potential therapies.

[Cognitive impairment in asthenic disorders]

The article presents a review of scientific publications devoted to cognitive aspects of asthenic disorders. The authors present different views on the etiology and basic mechanisms of pathogenesis of psychogenic asthenia and chronic fatigue syndrome, current diagnostic criteria for these diseases. The main attention is paid to the consideration of the neurocognitive deficit observed in mental asthenia and chronic fatigue syndrome. The role of cognitive control impairment in the development of adaptation disorders and the formation of asthenic conditions is considered. The results of studies of the effectiveness of pharmacological therapy for asthenic disorders are presented.

"A bit of a cough, tired, not very resilient - is that already Long-COVID?" perceptions and experiences of GPs with Long-COVID in year three of the pandemic. a qualitative interview study in Austria

BACKGROUND

Long-COVID is a new multisectoral healthcare challenge. This study aims at understanding experiences, knowledge, attitudes and (information) needs that GPs had and have in relation to Long-COVID and how these evolved since the beginning of the COVID-19 pandemic.

METHODS

The study used an exploratory qualitative research design using semistructured interviews. A total of 30 semistructured interviews with GPs in different primary care settings (single practices, group practices, primary care centres) were conducted between February and July 2022. The data were analysed using qualitative thematic content analysis with the software Atlas.ti.

RESULTS

This is the first study that empirically investigated Long-COVID management by GPs in Austria during the third year of the pandemic. All GPs indicated having experience with Long-COVID. In cities, GPs tended to have slightly better networks with specialists. The GPs who already worked in teams tended to find the management of Long-COVID easier. The symptoms that the physicians described as Long-COVID symptoms corresponded to those described in the international literature, but it is unclear whether syndromes and symptomes such as Post-Exertional-Malaise, autonomic dysfunction such as postural tachycardia syndrome or Mast-Cell-Overactivation-Syndrom, and cognitive dysfunctions were also recognized and correctly classified since they were never mentioned. Most GPs reacted quickly by granting the needed sick leaves and by seeing and discussing with the patients often.The treatment of the patients is described as an enormous challenge and frustrating for patient and GP if the treatment does not yield to significantly improved health also due to the high costs for the patient.

CONCLUSION

Long-COVID will continue to preoccupy our health care systems for a long time to come, as new variants of COVID-19 will continue to produce new patients without adequate prevention strategies. Therefore, it is not a question of if but when good support for GPs and adequate care pathways for people with Long-COVID will be implemented. Specific contact points that are familiar with therapy-refractory postacute infection syndromes like the postacute COVID condition as a subgroup of Long-COVID are urgently needed.

Overlapping conditions in Long COVID at a multisite academic center

Background

Many patients experience persistent symptoms after COVID-19, a syndrome referred to as Long COVID (LC). The goal of this study was to identify novel new or worsening comorbidities self-reported in patients with LC.

Methods

Patients diagnosed with LC (n = 732) at the Mayo Long COVID Care Clinic in Rochester, Minnesota and Jacksonville, Florida were sent questionnaires to assess the development of new or worsening comorbidities following COVID-19 compared to patients with SARS-CoV-2 that did not develop LC (controls). Both groups were also asked questions screening for myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), generalized joint hypermobility (GJH) and orthostatic intolerance. 247 people with LC (33.7%) and 40 controls (50%) responded to the surveys.

Results

In this study LC patients averaged 53 years of age and were predominantly White (95%) women (75%). The greatest prevalence of new or worsening comorbidities following SARS-CoV-2 infection in patients with LC vs. controls reported in this study were pain (94.4% vs. 0%, p < 0.001), neurological (92.4% vs. 15.4%, p < 0.001), sleep (82.8% vs. 5.3%, p < 0.001), skin (69.8% vs. 0%, p < 0.001), and genitourinary (60.6% vs. 25.0%, p = 0.029) issues. 58% of LC patients screened positive for ME/CFS vs. 0% of controls (p < 0.001), 27% positive for GJH compared to 10% of controls (p = 0.026), and a positive average score of 4.0 on orthostatic intolerance vs. 0 (p < 0.001). The majority of LC patients with ME/CFS were women (77%).

Conclusion

We found that comorbidities across 12 surveyed categories were increased in patients following SARS-CoV-2 infection. Our data also support the overlap of LC with ME/CFS, GJH, and orthostatic intolerance. We discuss the pathophysiologic, research, and clinical implications of identifying these conditions with LC.

Immunometabolic changes and potential biomarkers in CFS peripheral immune cells revealed by single-cell RNA sequencing

The pathogenesis of Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) remains unclear, though increasing evidence suggests inflammatory processes play key roles. In this study, single-cell RNA sequencing (scRNA-seq) of peripheral blood mononuclear cells (PBMCs) was used to decipher the immunometabolic profile in 4 ME/CFS patients and 4 heathy controls. We analyzed changes in the composition of major PBMC subpopulations and observed an increased frequency of total T cells and a significant reduction in NKs, monocytes, cDCs and pDCs. Further investigation revealed even more complex changes in the proportions of cell subpopulations within each subpopulation. Gene expression patterns revealed upregulated transcription factors related to immune regulation, as well as genes associated with viral infections and neurodegenerative diseases.CD4+ and CD8+ T cells in ME/CFS patients show different differentiation states and altered trajectories, indicating a possible suppression of differentiation. Memory B cells in ME/CFS patients are found early in the pseudotime, indicating a unique subtype specific to ME/CFS, with increased differentiation to plasma cells suggesting B cell overactivity. NK cells in ME/CFS patients exhibit reduced cytotoxicity and impaired responses, with reduced expression of perforin and CD107a upon stimulation. Pseudotime analysis showed abnormal development of adaptive immune cells and an enhanced cell-cell communication network converging on monocytes in particular. Our analysis also identified the estrogen-related receptor alpha (ESRRA)-APP-CD74 signaling pathway as a potential biomarker for ME/CFS in peripheral blood. In addition, data from the GSE214284 database confirmed higher ESRRA expression in the monocyte cell types of male ME/CFS patients. These results suggest a link between immune and neurological symptoms. The results support a disease model of immune dysfunction ranging from autoimmunity to immunodeficiency and point to amyloidotic neurodegenerative signaling pathways in the pathogenesis of ME/CFS. While the study provides important insights, limitations include the modest sample size and the evaluation of peripheral blood only. These findings highlight potential targets for diagnostic biomarkers and therapeutic interventions. Further research is needed to validate these biomarkers and explore their clinical applications in managing ME/CFS.

Long COVID and hypermobility spectrum disorders have shared pathophysiology

Hypermobility spectrum disorders (HSD) and hypermobile Ehlers-Danlos syndrome (hEDS) are the most common joint hypermobility conditions encountered by physicians, with hypermobile and classical EDS accounting for >90% of all cases. Hypermobility has been detected in up to 30-57% of patients with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), fibromyalgia, postural orthostatic tachycardia syndrome (POTS), and long COVID (LC) compared to the general population. Extrapulmonary symptoms, including musculoskeletal pain, dysautonomia disorders, cognitive disorders, and fatigue, are seen in both LC and HSD. Additionally, ME/CFS has overlapping symptoms with those seen in HSD. Mast cell activation and degranulation occurring in both LC and ME/CFS may result in hyperinflammation and damage to connective tissue in these patients, thereby inducing hypermobility. Persistent inflammation may result in the development or worsening of HSD. Hence, screening for hypermobility and other related conditions including fibromyalgia, POTS, ME/CFS, chronic pain conditions, joint pain, and myalgia is essential for individuals experiencing LC. Pharmacological treatments should be symptom-focused and geared to a patient's presentation. Paced exercise, massage, yoga, and meditation may also provide benefits.

The relation between FT3 and long-term fatigue in patients with COVID-19

Background

Under the current pandemic of Corona Virus Disease 2019 (COVID-19), The relationship between fatigue and COVID-19 has been found. Infection with COVID-19 is associated with fatigue long after the acute phase of COVID-19. Understanding the association of thyroid hormones levels with post-COVID condition, such as fatigue, is necessary to improve quality of life.

Methods

This population-based cohort study was conducted in Dalian, China, from December 2022, to March 2023, using a Yidu Core platform in the First Affiliated Hospital of Dalian Medical University, that integrates medical records, laboratory tests, and all diagnosis and treatment information based on patients in hospital. Eligible individuals were 40 patients with COVID-19, Divided them into fatigue group and non-fatigue group following up by telephone using the FS-14 scale after 6 months. The primary outcomes were the diagnoses of fatigue. The association between thyroid hormones levels and post-COVID condition, such as fatigue, was assessed using logistic regression analysis.

Results

Compared with the non-fatigue group, the FT3 level in fatigue group was lower (p<0.05). FT3 was negatively correlated with fatigue after 6 months (OR 0.257, p<0.05). After adjusting for confounding factors such as age and gender, low FT3 was a risk factor for fatigue in patients with COVID-19, (OR 0.225, p<0.05). And the FT3 is less than 2.47 mol/L, it is the best critical value for predicting long-term fatigue, with a sensitivity of 92.3% and a specificity of 48.1%.

Conclusions

Most people still have fatigue 6 months after COVID-19 infection. FT3 serves as the important index to predict fatigue in patients with COVID-19. it should be closely monitored during infection.

Long COVID science, research and policy

Long COVID represents the constellation of post-acute and long-term health effects caused by SARS-CoV-2 infection; it is a complex, multisystem disorder that can affect nearly every organ system and can be severely disabling. The cumulative global incidence of long COVID is around 400 million individuals, which is estimated to have an annual economic impact of approximately $1 trillion-equivalent to about 1% of the global economy. Several mechanistic pathways are implicated in long COVID, including viral persistence, immune dysregulation, mitochondrial dysfunction, complement dysregulation, endothelial inflammation and microbiome dysbiosis. Long COVID can have devastating impacts on individual lives and, due to its complexity and prevalence, it also has major ramifications for health systems and economies, even threatening progress toward achieving the Sustainable Development Goals. Addressing the challenge of long COVID requires an ambitious and coordinated-but so far absent-global research and policy response strategy. In this interdisciplinary review, we provide a synthesis of the state of scientific evidence on long COVID, assess the impacts of long COVID on human health, health systems, the economy and global health metrics, and provide a forward-looking research and policy roadmap.