Postacute COVID-19 is Characterized by Gut Viral Antigen Persistence in Inflammatory Bowel Diseases

Long COVID: A Systematic Review of Preventive Strategies

Background: Since the emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in December 2019, long COVID (LC) has become a significant global health burden. While knowledge about LC is accumulating, studies on its prevention are still lacking. Methods: We conducted a systematic review following the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines to investigate prevention options for LC. We identified fifteen articles on vaccines, seven on antivirals, and six on other interventions after searching for articles in the PubMed/MEDLINE database using the MeSH terms. Results: Most vaccine-related studies demonstrated a protective effect of COVID-19 vaccines against developing LC. Our review found an equivocal effect of antivirals, while metformin had a protective effect in outpatients and corticosteroids were protective in hospitalized patients against LC. Conversely, COVID-19 convalescent plasma and multiple micronutrient supplement did not confer any protection against LC. Conclusions: COVID-19 vaccination is vital as it not only prevents COVID-19 but also reduces the severity of illness and may help prevent LC. Further studies are warranted to shed light on preventive strategies for long COVID.

Long COVID and endometriosis: a systematic review and meta-analysis

Long COVID conditions entail the persistence of COVID-19-related symptoms for at least eight weeks following SARS-CoV-2 infection. The prevalence of long COVID is estimated to range from 10 to 30% among individuals infected with SARS-CoV-2. Despite its growing impact on healthcare systems, long COVID remains poorly understood. In parallel, endometriosis, a chronic inflammatory condition affecting around 10% of reproductive-age women, is marked by symptoms such as pelvic pain and infertility. The aim of this study was to assess the association between endometriosis and long COVID. We performed a systematic review of long COVID among endometriosis patients in Pubmed/Medline, Cochran Library and Science Direct databases from inception to August 2023. We independently selected studies, extracted data, assessed risk of bias, and compared endometriosis versus non endometriosis patients for long. Pooled analyses were based on random-effect models, and the I2 statistic was used to quantify heterogeneity across studies. A total of 2 cross-sectional studies (N = 216,095 participants) were included. The pooled analysis comparing endometriosis to non-endometriosis patients significantly showed association for long COVID (pooled RR = 1.41 [1.31-1.52], I2 = 29%, p < 0.001). Women, who are disproportionately affected by long COVID, particularly those with endometriosis, may face compounded health challenges. While our findings suggest a possible association between endometriosis and long COVID, the evidence is currently limited to two observational studies. Further research involving diverse populations and robust study designs is needed to confirm this relationship and clarify underlying mechanisms.

Gastrointestinal Barrier Disruption in Post-COVID Syndrome Fatigue Patients

BACKGROUND

Post-COVID Syndrome (PCS) is the term for a condition with persistent symptoms in a proportion of COVID-19 patients after asymptomatic, mild, or severe disease courses. Numbers vary, but the current estimate is that after COVID-19 approximately 10% develop PCS. The aim of our study was to evaluate the impact of SARS-CoV-2 infection on the gastrointestinal (GI) tract and associations with the development of PCS with fatigue, post-exertional malaise (PEM), orthostatic dysregulation, autonomous dysregulation, and/or neurocognitive dysregulation.

METHODS

By combining medical record data from a prospective observational study with symptom analysis before, during, and after SARS-CoV-2 infection, we aimed to identify potential risk factors and predictive markers for PCS. Additionally, we analyzed blood, saliva, and stool samples from this well-characterized PCS patient cohort to biologically validate our findings.

RESULTS

We identified significant associations between pre-existing GI complaints and the development of PCS Fatigue. PCS patients showed higher LBP/sCD14 ratios, lower IL-33 levels, and higher IL-6 levels compared to control groups. Our results highlight the critical role of the GI tract in PCS development of post-viral Fatigue.

CONCLUSION

We propose that the viral infection disrupts pathways related to the innate immune response and GI barrier function, evidenced by intestinal low-grade inflammation and GI barrier leakage. Monitoring GI symptoms and markers before, during, and after SARS-CoV-2 infection is crucial for identifying predictive clinical phenotypes in PCS. Understanding the interaction between viral infections, immune responses, and gut integrity could lead to more effective diagnostic and treatment strategies, ultimately reducing the burden on PCS patients.

Association of Vitamin D Supplementation with Glutathione Peroxidase (GPx) Activity, Interleukine-6 (IL-6) Levels, and Anxiety and Depression Scores in Patients with Post-COVID-19 Condition

Coronavirus disease 2019 (COVID-19) presents with various symptoms, and some patients develop post-COVID-19 condition (PCC). Vitamin D has shown therapeutic potential in COVID-19 and may offer benefits for PCC. The aim of this study was to evaluate the differences associated with two supplementation strategies (bolus and daily) on interleukin-6 (IL-6) levels, glutathione peroxidase (GPx) activity, and clinical outcomes in PCC patients, regardless of whether target 25 (OH) D levels reached the ideal range. We conducted a self-controlled study in which 54 participants with PCC were supplemented with vitamin D3 (n = 28 bolus and n = 26 daily) for 2 months. Blood samples were collected to measure IL-6 levels and GPx activity using spectrophotometric methods. The Hospital Anxiety and Depression Scale (HADS) was used to assess mental function. Both bolus and daily vitamin D supplementation were significantly associated with increased GPx activity and decreased IL-6 levels. Daily supplementation was additionally associated with a significant reduction in anxiety and depression scores. However, neither regimen was associated with improvements in cough, dyspnea, or fatigue. These findings suggest a potential association between vitamin D supplementation and improvements in antioxidant and neuropsychiatric parameters in PCC, possibly mediated by its immunomodulatory and antioxidant properties. Further placebo-controlled trials are warranted to determine whether these observed associations reflect causal relationships.

Targeting the SARS-CoV-2 reservoir in long COVID

There are no approved treatments for post-COVID-19 condition (also known as long COVID), a debilitating disease state following SARS-CoV-2 infection that is estimated to affect tens of millions of people. A growing body of evidence shows that SARS-CoV-2 can persist for months or years following COVID-19 in a subset of individuals, with this reservoir potentially driving long-COVID symptoms or sequelae. There is, therefore, an urgent need for clinical trials targeting persistent SARS-CoV-2, and several trials of antivirals or monoclonal antibodies for long COVID are underway. However, because mechanisms of SARS-CoV-2 persistence are not yet fully understood, such studies require important considerations related to the mechanism of action of candidate therapeutics, participant selection, duration of treatment, standardisation of reservoir-associated biomarkers and measurables, optimal outcome assessments, and potential combination approaches. In addition, patient subgroups might respond to some interventions or combinations of interventions, making post-hoc analyses crucial. Here, we outline these and other key considerations, with the goal of informing the design, implementation, and interpretation of trials in this rapidly growing field. Our recommendations are informed by knowledge gained from trials targeting the HIV reservoir, hepatitis C, and other RNA viruses, as well as precision oncology, which share many of the same hurdles facing long-COVID trials.

The consequences of SARS-CoV-2 within-host persistence

SARS-CoV-2 causes an acute respiratory tract infection that resolves in most people in less than a month. Yet some people with severely weakened immune systems fail to clear the virus, leading to persistent infections with high viral titres in the respiratory tract. In a subset of cases, persistent SARS-CoV-2 replication results in an accelerated accumulation of adaptive mutations that confer escape from neutralizing antibodies and enhance cellular infection. This may lead to the evolution of extensively mutated SARS-CoV-2 variants and introduce an element of chance into the timing of variant evolution, as variant formation may depend on evolution in a single person. Whether long COVID is also caused by persistence of replicating SARS-CoV-2 is controversial. One line of evidence is detection of SARS-CoV-2 RNA and proteins in different body compartments long after SARS-CoV-2 infection has cleared from the upper respiratory tract. However, thus far, no replication competent virus has been cultured from individuals with long COVID who are immunocompetent. In this Review, we consider mechanisms of viral persistence, intra-host evolution in persistent infections, the connection of persistent infections with SARS-CoV-2 variants and the possible role of SARS-CoV-2 persistence in long COVID. Understanding persistent infections may therefore resolve much of what is still unclear in COVID-19 pathophysiology, with possible implications for other emerging viruses.

SARS-CoV-2 Spike Protein and Long COVID-Part 1: Impact of Spike Protein in Pathophysiological Mechanisms of Long COVID Syndrome

SARS-CoV-2 infection has resulted in more than 700 million cases and nearly 7 million deaths worldwide. Although vaccination efforts have effectively reduced mortality and transmission rates, a significant proportion of recovered patients-up to 40%-develop long COVID syndrome (LC) or post-acute sequelae of COVID-19 infection (PASC). LC is characterized by the persistence or emergence of new symptoms following initial SARS-CoV-2 infection, affecting the cardiovascular, neurological, respiratory, gastrointestinal, reproductive, and immune systems. Despite the broad range of clinical symptoms that have been described, the risk factors and pathogenic mechanisms behind LC remain unclear. This review, the first of a two-part series, is distinguished by the discussion of the role of the SARS-CoV-2 spike protein in the primary mechanisms underlying the pathophysiology of LC.

A multidisciplinary review of long COVID to address the challenges in diagnosis and updated management guidelines

Long COVID has emerged as a significant challenge since the COVID-19 pandemic, which was declared as an outbreak in March 2020, marked by diverse symptoms and prolonged duration of disease. Defined by the WHO as symptoms persisting or emerging for at least two months post-SARS-CoV-2 infection without an alternative cause, its prevalence varies globally, with estimates of 10-20% in Europe, 7.3% in the USA, and 3.0% in the UK. The condition's etiology remains unclear, involving factors, such as renin-angiotensin system overactivation, persistent viral reservoirs, immune dysregulation, and autoantibodies. Reactivated viruses, like EBV and HSV-6, alongside epigenetic alterations, exacerbate mitochondrial dysfunction and energy imbalance. Emerging evidence links SARS-CoV-2 to chromatin and gut microbiome changes, further influencing long-term health impacts. Diagnosis of long COVID requires detailed systemic evaluation through medical history and physical examination. Management is highly individualized, focusing mainly on the patient's symptoms and affected systems. A multidisciplinary approach is essential, integrating diverse perspectives to address systemic manifestations, underlying mechanisms, and therapeutic strategies. Enhanced understanding of long COVID's pathophysiology and clinical features is critical to improving patient outcomes and quality of life. With a growing number of cases expected globally, advancing research and disseminating knowledge on long COVID remain vital for developing effective diagnostic and management frameworks, ultimately supporting better care for affected individuals.

Long-term Sequelae Following Dengue Infection vs SARS-CoV-2 Infection in a Pediatric Population: A Retrospective Cohort Study

Background

Long-term postacute sequelae following SARS-CoV-2 infection in children have been extensively documented. However, while persistence of chronic symptoms following pediatric dengue infection has been documented in small prospective cohorts, population-based studies are limited. We evaluated the risk of multisystemic complications following dengue infection in contrast to that after SARS-CoV-2 infection in a multiethnic pediatric Asian population.

Methods

This retrospective population-based cohort study utilized national COVID-19/dengue registries to construct cohorts of Singaporean children aged 1 to 17 years with either laboratory-confirmed dengue infection from 1 January 2017 to 31 October 2022 or confirmed SARS-CoV-2 infection from 1 July 2021 to 31 October 2022. Cox regression was utilized to estimate risks of new-incident cardiovascular, neurologic, gastrointestinal, autoimmune, and respiratory complications, as identified by national health care claims data, at 31 to 300 days after dengue infection vs COVID-19. Risks were reported by 2 measures: adjusted hazard ratio (aHR) and excess burden.

Results

This study included 6452 children infected with dengue and 260 749 cases of COVID-19. Among children infected with dengue, there was increased risk of any postacute gastrointestinal sequelae (aHR, 2.98; 95% CI, 1.18-7.18), specifically appendicitis (aHR, 3.50; 95% CI, 1.36-8.99), when compared with children infected with SARS-CoV-2. In contrast to cases of unvaccinated COVID-19, children infected with dengue demonstrated lower risk (aHR, 0.42; 95% CI, .29-.61) and excess burden (-6.50; 95% CI, -9.80 to -3.20) of any sequelae, as well as lower risk of respiratory sequelae (aHR, 0.17; 95% CI, .09-.31).

Conclusions

Lower overall risk of postacute complications was observed in children following dengue infection vs COVID-19; however, higher risk of appendicitis was reported 31 to 300 days after dengue infection vs SARS-CoV-2. Public health strategies to mitigate the impact of dengue and COVID-19 in children should consider the possibility of chronic postinfectious sequelae.

Long COVID: Pathophysiology, current concepts, and future directions

Long COVID, an umbrella term referring to a variety of symptoms and clinical presentations that emerges in a subset of patients after severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, has a significant effect on quality of life and places a substantial burden on health care systems worldwide, straining financial and human resources. The pathophysiology of long COVID remains incompletely understood, though several hypotheses have been proposed to explain different aspects of this complex condition. SARS-CoV-2 persistence, direct organ damage, innate and adaptive immune system perturbation, autoimmunity, latent virus reactivation, endothelial dysfunction, and microbiome disturbances are among the most relevant avenues for elucidating the evolution, complexity, and mechanisms of long COVID. Active investigation regarding potential biomarkers for long COVID and its associated disease endotypes highlights the role of inflammatory mediators, immunophenotyping, and multiomics approaches. Further advances in understanding long COVID are needed to inform current and future therapeutics.

Impact of Glucose, Inflammation and Phytochemicals on ACE2, TMPRSS2 and Glucose Transporter Gene Expression in Human Intestinal Cells

Inflammation is associated with the pathophysiology of type 2 diabetes and COVID-19. Phytochemicals have the potential to modulate inflammation, expression of SARS-CoV-2 viral entry receptors (angiotensin-converting enzyme 2 (ACE2) and transmembrane protease, serine 2 (TMPRSS2)) and glucose transport in the gut. This study assessed the impact of phytochemicals on these processes. We screened 12 phytochemicals alongside 10 pharmaceuticals and three plant extracts, selected for known or hypothesised effects on the SARS-CoV-2 receptors and COVID-19 risk, for their effects on the expression of ACE2 or TMPRSS2 in differentiated Caco-2/TC7 human intestinal epithelial cells. Genistein, apigenin, artemisinin and sulforaphane were the most promising ones, as assessed by the downregulation of TMPRSS2, and thus they were used in subsequent experiments. The cells were then co-stimulated with pro-inflammatory cytokines interleukin-1 beta (IL-1β) and tumour necrosis factor-alpha (TNF-α) for ≤168 h to induce inflammation, which are known to induce multiple pathways, including the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) pathway. Target gene expression (ACE2, TMPRSS2, SGLT1 (sodium-dependent glucose transporter 1) and GLUT2 (glucose transporter 2)) was measured by droplet digital PCR, while interleukin-1 (IL-6), interleukin-1 (IL-8) and ACE2 proteins were assessed using ELISA in both normal and inflamed cells. IL-1β and TNF-α treatment upregulated ACE2, TMPRSS2 and SGLT1 gene expression. ACE2 increased with the duration of cytokine exposure, coupled with a significant decrease in IL-8, SGLT1 and TMPRSS2 over time. Pearson correlation analysis revealed that the increase in ACE2 was strongly associated with a decrease in IL-8 (r = -0.77, p < 0.01). The regulation of SGLT1 gene expression followed the same pattern as TMPRSS2, implying a common mechanism. Although none of the phytochemicals decreased inflammation-induced IL-8 secretion, genistein normalised inflammation-induced increases in SGLT1 and TMPRSS2. The association between TMPRSS2 and SGLT1 gene expression, which is particularly evident in inflammatory conditions, suggests a common regulatory pathway. Genistein downregulated the inflammation-induced increase in SGLT1 and TMPRSS2, which may help lower the postprandial glycaemic response and COVID-19 risk or severity in healthy individuals and those with metabolic disorders.

Serum Spike Protein Persistence Post COVID Is Not Associated with ME/CFS

Background/Objectives: According to the World Health Organization (WHO) and Centers for Disease Control and Prevention (CDC), an estimated 3-6% of people suffer from post-COVID condition or syndrome (PCS). A subset meets the diagnostic criteria for myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). Studies have reported that SARS-CoV-2 proteins or RNA can persist after acute infection in serum or tissues, but their role in PCS is unclear. Methods: Here, SARS-CoV-2 spike protein was analyzed in the serum of 121 PCS patients with predominant fatigue and exertional intolerance, of whom 72 met diagnostic criteria for ME/CFS, 37 post-COVID recovered healthy controls, and 32 pre-pandemic healthy controls. Results: Spike protein was detected in the serum of 11% of recovered controls, 2% of PCS patients, and 14% of ME/CFS patients between 4 and 31 months after SARS-CoV-2 infection, but not in pre-pandemic samples. The occurrence and concentration of spike protein did not correlate with infection or vaccination timepoints. In ME/CFS patients, spike protein presence was not associated with the severity of symptoms or functional disability. In 5 out of 22 patients who under-went immunoglobulin depletion, spike protein levels were reduced or undetectable after treatment, indicating binding to immunoglobulins. Conclusions: In summary, this study identified serum spike protein in a subset of patients but found no association with ME/CFS.

Upregulation of olfactory receptors and neuronal-associated genes highlights complex immune and neuronal dysregulation in Long COVID patients

A substantial portion of patients infected with SARS-CoV-2 experience prolonged complications, known as Long COVID (LC). A subset of these patients exhibits the most debilitating symptoms, similar to those defined in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS). We performed bulk RNA sequencing (RNAseq) on the whole blood of LC with ME/CFS, at least 12 months post-onset of the acute disease, and compared them with controls. We found that LC patients had a distinct transcriptional profile compared to controls. Key findings include the upregulation of genes involved in immune dysregulation and neuronal development, such as Fezf2, BRINP2, HOXC12, MEIS2, ZFHX3, and RELN. These genes are linked to neuroinflammatory responses, cognitive impairments, and hematopoietic disturbances, suggesting ongoing neurological and immune disturbances in LC patients. RELN, encoding the Reelin protein, was notably elevated in LC patients, potentially serving as a biomarker for LC pathogenesis due to its role in inflammation and neuronal function. Immune cell analysis showed altered profiles in LC patients, with increased activated memory CD4 + T cells and neutrophils, and decreased regulatory T cells and NK cells, reflecting immune dysregulation. Changes in cytokine and chemokine expression further underscore the chronic inflammatory state in LC patients. Notably, a unique upregulation of olfactory receptors (ORs) suggest alternative roles for ORs in non-olfactory tissues. Pathway analysis revealed upregulation in ribosomal RNA processing, amino acid metabolism, protein synthesis, cell proliferation, DNA repair, and mitochondrial pathways, indicating heightened metabolic and immune demands. Conversely, downregulated pathways, such as VEGF signaling and TP53 activity, point to impaired tissue repair and cellular stress responses. Overall, our study underscores the complex interplay between immune and neuronal dysfunction in LC patients, providing insights into potential diagnostic biomarkers and therapeutic targets. Future research is needed to fully understand the roles and interactions of these genes in LC pathophysiology.

Animal Models for Long COVID: Current Advances, Limitations, and Future Directions

Long COVID (LC) represents a chronic, systemic, and often disabling condition that poses a significant ongoing threat to public health. Foundational scientific studies are needed to unravel the underlying mechanisms, with the ultimate goal of developing effective preventative and therapeutic strategies. Therefore, there is an urgent demand for animal models that can accurately replicate the clinical features of LC. This review integrates clinical epidemiological data to summarize the pathological changes in extrapulmonary systems involved in LC. Additionally, it critically examines the capacity of existing animal models, including nonhuman primates, genetically modified mice, and Syrian hamsters, to exhibit enduring postinfection symptoms that align with human clinical manifestations, and identifies key areas requiring further development. The objective is to offer insights that will aid in the development of next-generation animal models, thereby accelerating our understanding of how acute respiratory viral infections transition into chronic conditions, and ensuring preparedness for future pandemics.

Cerebromicrovascular mechanisms contributing to long COVID: implications for neurocognitive health

Long COVID (also known as post-acute sequelae of SARS-CoV-2 infection [PASC] or post-COVID syndrome) is characterized by persistent symptoms that extend beyond the acute phase of SARS-CoV-2 infection, affecting approximately 10% to over 30% of those infected. It presents a significant clinical challenge, notably due to pronounced neurocognitive symptoms such as brain fog. The mechanisms underlying these effects are multifactorial, with mounting evidence pointing to a central role of cerebromicrovascular dysfunction. This review investigates key pathophysiological mechanisms contributing to cerebrovascular dysfunction in long COVID and their impacts on brain health. We discuss how endothelial tropism of SARS-CoV-2 and direct vascular infection trigger endothelial dysfunction, impaired neurovascular coupling, and blood-brain barrier disruption, resulting in compromised cerebral perfusion. Furthermore, the infection appears to induce mitochondrial dysfunction, enhancing oxidative stress and inflammation within cerebral endothelial cells. Autoantibody formation following infection also potentially exacerbates neurovascular injury, contributing to chronic vascular inflammation and ongoing blood-brain barrier compromise. These factors collectively contribute to the emergence of white matter hyperintensities, promote amyloid pathology, and may accelerate neurodegenerative processes, including Alzheimer's disease. This review also emphasizes the critical role of advanced imaging techniques in assessing cerebromicrovascular health and the need for targeted interventions to address these cerebrovascular complications. A deeper understanding of the cerebrovascular mechanisms of long COVID is essential to advance targeted treatments and mitigate its long-term neurocognitive consequences.

Review of organ damage from COVID and Long COVID: a disease with a spectrum of pathology

Long COVID, as currently defined by the World Health Organization (WHO) and other authorities, is a symptomatic condition that has been shown to affect an estimated 10 %-30 % of non-hospitalized patients after one infection. However, COVID-19 can also cause organ damage in individuals without symptoms, who would not fall under the current definition of Long COVID. This organ damage, whether symptomatic or not, can lead to various health impacts such as heart attacks and strokes. Given these observations, it is necessary to either expand the definition of Long COVID to include organ damage or recognize COVID-19-induced organ damage as a distinct condition affecting many symptomatic and asymptomatic individuals after COVID-19 infections. It is important to consider that many known adverse health outcomes, including heart conditions and cancers, can be asymptomatic until harm thresholds are reached. Many more medical conditions can be identified by testing than those that are recognized through reported symptoms. It is therefore important to similarly recognize that while Long COVID symptoms are associated with organ damage, there are many individuals that have organ damage without displaying recognized symptoms and to include this harm in the characterization of COVID-19 and in the monitoring of individuals after COVID-19 infections.

N-acetylcysteine (NAC) supplementation improves dyspnea and may normalize von Willebrand plasma levels in gynecologic patients with Post-Acute-COVID-Sequela (PASC)/Long COVID

Objectives

A subset of COVID-infected cancer patients may develop post-acute sequelae of COVID-19 (PASC), also known as Long COVID (LC). While LC is considered multifactorial in its pathogenesis, growing evidence suggests that persistent microvascular inflammation (ie, spike-induced endotheliosis) causing chronically elevated levels of clotting factors including von Willebrand factor (vWF), clumping/clotting of red blood cells and platelets, and thrombotic complications may be at the root of PASC/LC symptoms. N-Acetylcysteine (NAC), a precursor of glutathione, is an inexpensive FDA-approved drug/supplement endowed with mucolytic, antioxidant, anti-inflammatory and thrombolytic properties. Multiple reports have recently demonstrated the potential clinical activity of NAC in COVID-19 patients. We retrospectively evaluated responses to NAC supplementation in a total of 9 PASC/LC patients, 3 of which reporting regular use of NAC, followed in our Gynecologic Oncology clinic.

Methods

Gynecologic patients using NAC supplement (3 patients) vs controls (6 patients) with persistent LC/PASC symptoms and with elevated plasmatic vWF levels were identified in our Gynecologic Oncology clinic database and evaluated for improvement/normalization in LC/PASC symptoms and vWF levels.

Results

Subjective improvement in shortness of breath, brain fog and fatigue with normalization of vWF levels were noted in 3 out of 3 PASC/LC patients using oral NAC (600-1200 mg BID) vs none of the randomly selected cancer control patients with PASC/LC (Fisher's exact P = 0.0119).

Conclusions

These preliminary results suggest that NAC may represent an inexpensive, safe and potentially effective supplement to improve many PASC/LC-related symptoms. Prospective randomized studies with NAC in PASC/LC patients are needed to confirm these findings.

Animal Models of Non-Respiratory, Post-Acute Sequelae of COVID-19

Post-acute sequelae of COVID-19 (PASC) are a diverse set of symptoms and syndromes driven by dysfunction of multiple organ systems that can persist for years and negatively impact the quality of life for millions of individuals. We currently lack specific therapeutics for patients with PASC, due in part to an incomplete understanding of its pathogenesis, especially for non-pulmonary sequelae. Here, we discuss three animal models that have been utilized to investigate PASC: non-human primates (NHPs), hamsters, and mice. We focus on neurological, gastrointestinal, and cardiovascular PASC and highlight advances in mechanistic insight that have been made using these animal models, as well as discussing the sequelae that warrant continued and intensive research.

Mucosal immune response in biology, disease prevention and treatment

The mucosal immune system, as the most extensive peripheral immune network, serves as the frontline defense against a myriad of microbial and dietary antigens. It is crucial in preventing pathogen invasion and establishing immune tolerance. A comprehensive understanding of mucosal immunity is essential for developing treatments that can effectively target diseases at their entry points, thereby minimizing the overall impact on the body. Despite its importance, our knowledge of mucosal immunity remains incomplete, necessitating further research. The outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has underscored the critical role of mucosal immunity in disease prevention and treatment. This systematic review focuses on the dynamic interactions between mucosa-associated lymphoid structures and related diseases. We delve into the basic structures and functions of these lymphoid tissues during disease processes and explore the intricate regulatory networks and mechanisms involved. Additionally, we summarize novel therapies and clinical research advances in the prevention of mucosal immunity-related diseases. The review also addresses the challenges in developing mucosal vaccines, which aim to induce specific immune responses while maintaining tolerance to non-pathogenic microbes. Innovative therapies, such as nanoparticle vaccines and inhalable antibodies, show promise in enhancing mucosal immunity and offer potential for improved disease prevention and treatment.

Low-Grade Inflammation in Long COVID Syndrome Sustains a Persistent Platelet Activation Associated With Lung Impairment

In the present study, we provide evidence on the potential mechanisms involved in the residual pulmonary impairment described in long COVID syndrome. Data highlight that lung damage is significantly associated with a proinflammatory platelet phenotype, characterized mainly by the formation of platelet-leukocyte aggregates. In ex vivo experiments, long COVID plasma reproduces the platelet activation observed in vivo and highlights low-grade inflammation as a potential underpinning mechanism, exploiting a synergistic activity between C-reactive protein and subthreshold concentrations of interleukin-6. The platelet-activated phenotype is blunted by anti-inflammatory and antiplatelet drugs, suggesting a potential therapeutic option in this clinical setting.

Potential Biomarkers for Predicting the Risk of Developing Into Long COVID After COVID-19 Infection

BACKGROUND

Long COVID, a heterogeneous condition characterized by a range of physical and neuropsychiatric presentations, can be presented with a proportion of COVID-19-infected individuals.

METHODS

Transcriptomic data sets of those within gene expression profiles of COVID-19, long COVID, and healthy controls were retrieved from the GEO database. Differentially expressed genes (DEGs) falling under COVID-19 and long COVID were identified with R packages, and contemporaneously conducted module detection was performed with the Modular Pharmacology Platform (http://112.86.129.72:48081/). The integration of both DEGs and differentially expressed module-genes (DEMGs) regarding long COVID and COVID-19 was intersected by following Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), and Gene Set Enrichment Analysis (GSEA).

RESULTS

There were 11 and 62 differentially expressed modules, 1837 and 179 DEGs, as well as 103 and 508 DEMGs acquiring identified for both COVID-19 and long COVID, notably enriched in the immune-correlated signaling pathways. The immune infiltrating cells of long COVID and COVID-19 were comparatively and respectively assessed via CIBERSORT, ssGSEA, and xCell algorithms. Subsequently, the screening of hub genes involved employing the SVM-RFE, RF, XGBoost algorithms, and logistic regression analysis. Among the 67 candidate genes were processed with machine learning algorithms and logistic regression, a subgroup consisting of CEP55, CDCA2, MELK, and DEPDC1B, was at last identified as potential biomarkers for predicting the risk of the progression into long COVID after COVID-19 infections. The predicting performance of the potential biomarkers was quantified with a ROC value of 0.8762542, which proved the combination of potential biomarkers provided the highest performance.

CONCLUSIONS

In summary, we identified a subgroup of potential biomarkers for predicting the risk of the progression into long COVID after COVID-19 infection, which could be partly elucidation of the associated molecular mechanisms for long COVID.

Gut microbiota in post-acute COVID-19 syndrome: not the end of the story

The coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), has led to major global health concern. However, the focus on immediate effects was assumed as the tip of iceberg due to the symptoms following acute infection, which was defined as post-acute COVID-19 syndrome (PACS). Gut microbiota alterations even after disease resolution and the gastrointestinal symptoms are the key features of PACS. Gut microbiota and derived metabolites disorders may play a crucial role in inflammatory and immune response after SARS-CoV-2 infection through the gut-lung axis. Diet is one of the modifiable factors closely related to gut microbiota and COVID-19. In this review, we described the reciprocal crosstalk between gut and lung, highlighting the participation of diet and gut microbiota in and after COVID-19 by destroying the gut barrier, perturbing the metabolism and regulating the immune system. Therefore, bolstering beneficial species by dietary supplements, probiotics or prebiotics and fecal microbiota transplantation (FMT) may be a novel avenue for COVID-19 and PACS prevention. This review provides a better understanding of the association between gut microbiota and the long-term consequences of COVID-19, which indicates modulating gut dysbiosis may be a potentiality for addressing this multifaceted condition.

Measurement of circulating viral antigens post-SARS-CoV-2 infection in a multicohort study

OBJECTIVES

To determine the proportion of individuals with detectable antigen in plasma or serum after SARS-CoV-2 infection and the association of antigen detection with postacute sequelae of COVID-19 (PASC) symptoms.

METHODS

Plasma and serum samples were collected from adults participating in four independent studies at different time points, ranging from several days up to 14 months post-SARS-CoV-2 infection. The primary outcome measure was to quantify SARS-CoV-2 antigens, including the S1 subunit of spike, full-length spike, and nucleocapsid, in participant samples. The presence of 34 commonly reported PASC symptoms during the postacute period was determined from participant surveys or chart reviews of electronic health records.

RESULTS

Of the 1569 samples analysed from 706 individuals infected with SARS-CoV-2, 21% (95% CI, 18-24%) were positive for either S1, spike, or nucleocapsid. Spike was predominantly detected, and the highest proportion of samples was spike positive (20%; 95% CI, 18-22%) between 4 and 7 months postinfection. In total, 578 participants (82%) reported at least one of the 34 PASC symptoms included in our analysis ≥1 month postinfection. Cardiopulmonary, musculoskeletal, and neurologic symptoms had the highest reported prevalence in over half of all participants, and among those participants, 43% (95% CI, 40-45%) on average were antigen-positive. Among the participants who reported no ongoing symptoms (128, 18%), antigen was detected in 28 participants (21%). The presence of antigen was associated with the presence of one or more PASC symptoms, adjusting for sex, age, time postinfection, and cohort (OR, 1.8; 95% CI, 1.4-2.2).

DISCUSSION

The findings of this multicohort study indicate that SARS-CoV-2 antigens can be detected in the blood of a substantial proportion of individuals up to 14 months after infection. While approximately one in five asymptomatic individuals was antigen-positive, roughly half of all individuals reporting ongoing cardiopulmonary, musculoskeletal, and neurologic symptoms were antigen-positive.

The Intestine in Acute and Long COVID: Pathophysiological Insights and Key Lessons

Post-Acute Sequelae of SARS-CoV-2 infection (PASC), commonly known as Long COVID, represents a significant and complex health challenge with a wide range of symptoms affecting multiple organ systems. This review examines the emerging evidence suggesting a critical role of the gut and gut-brain axis in the pathophysiology of Long COVID. It explores how changes in the gut microbiome, disruption of gut barrier integrity, and the persistence of SARS-CoV-2 antigens within the gastrointestinal tract may contribute to the prolonged and varied symptoms seen in Long COVID, including chronic inflammation and neuropsychiatric disturbances. The review also summarizes key insights gained about Long COVID, highlighting its multifactorial nature, which involves immune dysregulation, microvascular damage, and autonomic nervous system dysfunction, with the gut playing a central role in these processes. While progress has been made in understanding these mechanisms, current evidence remains inconclusive. The challenges of establishing causality, standardizing research methodologies, and addressing individual variations in the microbiome are discussed, emphasizing the need for further longitudinal studies and more comprehensive approaches to enhance our understanding of these complex interactions. This review underscores the importance of personalized approaches in developing effective diagnostic and therapeutic strategies for Long COVID, while also acknowledging the significant gaps in our current understanding. Future research should aim to further unravel the complex interplay between the gut and Long COVID, ultimately improving outcomes for those affected by this condition.

Post-acute sequelae of SARS-CoV-2 infection (Long COVID) in older adults

Long COVID, also known as PASC (post-acute sequelae of SARS-CoV-2), is a complex infection-associated chronic condition affecting tens of millions of people worldwide. Many aspects of this condition are incompletely understood. Among them is how this condition may manifest itself in older adults and how it might impact the older population. Here, we briefly review the current understanding of PASC in the adult population and examine what is known on its features with aging. Finally, we outline the major gaps and areas for research most germane to older adults.

Probiotic Therapy of Gastrointestinal Symptoms During COVID-19 Infection: A Randomized, Double-Blind, Placebo-Controlled, Remote Study

BACKGROUND

The novel coronavirus (SARS-CoV-2) led to gastrointestinal manifestations in up to 50% of cases, with diarrhea being common, and probiotics have been suggested as a potential treatment.

AIM

This study aimed to assess changes in the microbiome and the effects of a multispecies probiotic in patients with COVID-19 in home quarantine through a fully remote telemedical approach.

METHODS

Thirty patients were randomized to receive either the Ecologic AAD probiotic (Winclove Probiotics, Amsterdam, The Netherlands), on the market as OMNi-BiOTiC 10 (Allergosan, Austria), or a placebo for 30 days in a 2:1 ratio. Respiratory and gastrointestinal symptoms were monitored in 2-10-day intervals via online surveys, and five stool samples were collected during the 30-day study period for microbiome and metabolomics analyses. Twenty-four healthy volunteers served as controls.

RESULTS

Of the 30 patients, 26 completed this study (10 placebo, 16 probiotic). Patients reported respiratory symptoms and a diminished gastrointestinal quality of life, both of which improved significantly during the study period, irrespective of the intervention. Compared to controls, infected patients showed significant alterations in the fecal microbiome (p = 0.002), including an increase in Bacteroidetes and decreases in Christensenellaceae, Ruminococcaceae, and Gammaproteobacteria, along with metabolomic changes. Probiotic treatment significantly modulated the patients' microbiome beta diversity (p = 0.001) and introduced the Enterococcus faecium W54 strain. Symptoms, COVID-19-related taxa, and the fecal metabolome were not affected by the intervention.

CONCLUSIONS

Patients with mild COVID-19 disease in home quarantine exhibited respiratory symptoms, a reduced gastrointestinal quality of life, and changes in the fecal microbiome and metabolome.

Gastrointestinal manifestations of long COVID

Long COVID is estimated to have affected 6.9 % of US adults, 17.8 million people in the US alone, as of early 2023. While SARS-CoV-2 is primarily considered a respiratory virus, gastrointestinal (GI) symptoms are also frequent in patients with coronavirus disease 2019 (COVID-19) and in patients with Long COVID. The risk of developing GI symptoms is increased with increasing severity of COVID-19, the presence of GI symptoms in the acute infection, and psychological distress both before and after COVID-19. Persistence of the virus in the GI tract, ensuing inflammation, and alteration of the microbiome are all likely mediators of the effects of SARS Co-V-2 virus on the gut. These factors may all increase intestinal permeability and systemic inflammation. GI inflammation and dysbiosis can change the absorption and metabolism of tryptophan, an important neurotransmitter. Long COVID GI symptoms resemble a Disorder of Gut Brain Interaction (DGBI) such as post infection Irritable Bowel Syndrome (IBS). Current standards of treatment for IBS can guide our treatment of Long COVID patients. Dysautonomia, a frequent Long COVID condition affecting the autonomic nervous system, can also affect the GI tract, and must be considered in Long COVID patients with GI symptoms. Long COVID symptoms fall within the broader category of Infection Associated Chronic Conditions (IACCs). Research into the GI symptoms of Long COVID may further our understanding of other post infection chronic GI conditions, and elucidate the roles of therapeutic options including antivirals, probiotics, neuromodulators, and treatments of dysautonomia.

Translating insights into therapies for Long Covid

Long Covid is defined by a wide range of symptoms that persist after the acute phase of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Commonly reported symptoms include fatigue, weakness, postexertional malaise, and cognitive dysfunction, with many other symptoms reported. Symptom range, duration, and severity are highly variable and partially overlap with symptoms of myalgic encephalomyelitis/chronic fatigue syndrome and other post-acute infectious syndromes, highlighting opportunities to define shared mechanisms of pathogenesis. Potential mechanisms of Long Covid are diverse, including persistence of viral reservoirs, dysregulated immune responses, direct viral damage of tissues targeted by SARS-CoV-2, inflammation driven by reactivation of latent viral infections, vascular endothelium activation or dysfunction, and subsequent thromboinflammation, autoimmunity, metabolic derangements, microglial activation, and microbiota dysbiosis. The heterogeneity of symptoms and baseline characteristics of people with Long Covid, as well as the varying states of immunity and therapies given at the time of acute infection, have made etiologies of Long Covid difficult to determine. Here, we examine progress on preclinical models for Long Covid and review progress being made in clinical trials, highlighting the need for large human studies and further development of models to better understand Long Covid. Such studies will inform clinical trials that will define treatments to benefit those living with this condition.

Neuroinflammation in Post COVID-19 Sequelae: Neuroinvasion and Neuroimmune Crosstalk

The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in December 2019 triggered a swift global spread, leading to a devastating pandemic. Alarmingly, approximately one in four individuals diagnosed with coronavirus disease 2019 (COVID-19) experience varying degrees of cognitive impairment, raising concerns about a potential increase in neurological sequelae cases. Neuroinflammation seems to be the key pathophysiological hallmark linking mild respiratory COVID-19 to cognitive impairment, fatigue, and neurological sequelae in COVID-19 patients, highlighting the interaction between the nervous and immune systems following SARS-CoV-2 infection. Several hypotheses have been proposed to explain how the virus disrupts physiological pathways to trigger inflammation within the CNS, potentially leading to neuronal damage. These include neuroinvasion, systemic inflammation, disruption of the lung and gut-brain axes, and reactivation of latent viruses. This review explores the potential origins of neuroinflammation and the underlying neuroimmune cross-talk, highlighting important unanswered questions in the field. Addressing these fundamental issues could enhance our understanding of the virus's impact on the CNS and inform strategies to mitigate its detrimental effects.

A Systematic Review and Meta-Analysis: Adverse Inflammatory Bowel Disease Outcomes Following Acute COVID-19

Background and Aims

Respiratory viral infections have been implicated in the exacerbation of immune-mediated inflammatory diseases such as inflammatory bowel disease (IBD). To understand the impact of early SARS-CoV-2 variants on the risk of adverse IBD outcomes, we aimed to perform a meta-analysis of high-quality studies.

Methods

Cohort studies investigating adverse IBD outcomes (IBD flares, change in disease activity, change in medication, IBD-related hospitalization, and surgery) following COVID-19 were retrieved from MEDLINE and Embase. The Risk Of Bias In Nonrandomized Studies-of Exposure tool was used to assess risk of bias. Random effects model meta-analysis was used to calculate the hazard ratio (HR) for risk of adverse outcomes. Subgroup analysis was performed to estimate risk of outcomes for ulcerative colitis and Crohn's disease patients. Metaregression was performed for sex and duration of follow-up.

Results

Of the 3119 identified studies, 5 were included in the meta-analysis. A total of 34,977 IBD patients with COVID-19 and 53,270 IBD patients without recorded COVID-19 infection were identified. Two of the studies showed a high risk of bias. The random effects model did not show a statistically significant increase in the risk of adverse IBD outcomes following COVID infection (HR:1.05 [0.75-1.46]). There was no significant difference in adverse outcomes between Crohn's disease (HR: 0.91 [0.82-1.02]) and ulcerative colitis patients (HR: 0.83 [0.76-0.90]). Neither the proportion of male participants nor the mean duration of follow-up were found to be significant predictors of effect size.

Conclusion

In this systematic review and meta-analysis, we find that COVID-19 did not increase the risk of adverse IBD outcomes.

High prevalence of long COVID in anti-TPO positive euthyroid individuals with strongly elevated SARS-CoV-2-specific T cell responses and moderately raised anti-spike IgG levels 23 months post-infection

Introduction

Severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) infection, the causative agent of coronavirus disease 2019 (COVID-19), causes post-acute infection syndrome in a surprisingly large number of cases worldwide. This condition, also known as long COVID or post-acute sequelae of COVID-19, is characterized by extremely complex symptoms and pathology. There is a growing consensus that this condition is a consequence of virus-induced immune activation and the inflammatory cascade, with its prolonged duration caused by a persistent virus reservoir.

Methods

In this cross-sectional study, we analyzed the SARS-CoV-2-specific T cell response against the spike, nucleocapsid, and membrane proteins, as well as the levels of spike-specific IgG antibodies in 51 healthcare workers, categorized into long COVID or convalescent control groups based on the presence or absence of post-acute symptoms. Additionally, we compared the levels of autoantibodies previously identified during acute or critical COVID-19, including anti-dsDNA, anti-cardiolipin, anti-β2-glycoprotein I, anti-neutrophil cytoplasmic antibodies, and anti-thyroid peroxidase (anti-TPO). Furthermore, we analyzed the antibody levels targeting six nuclear antigens within the ENA-6 S panel, as positivity for certain anti-nuclear antibodies has recently been shown to associate not only with acute COVID-19 but also with long COVID. Finally, we examined the frequency of diabetes in both groups. Our investigations were conducted at an average of 18.2 months (convalescent control group) and 23.1 months (long COVID group) after confirmed acute COVID-19 infection, and an average of 21 months after booster vaccination.

Results

Our results showed significant differences between the two groups regarding the occurrence of acute infection relative to administering the individual vaccine doses, the frequency of acute symptoms, and the T cell response against all structural SARS-CoV-2 proteins. A statistical association was observed between the incidence of long COVID symptoms and highly elevated anti-TPO antibodies based on Pearson's chi-squared test. Although patients with long COVID showed moderately elevated anti-SARS-CoV-2 spike IgG serum antibody levels compared to control participants, and further differences were found regarding the positivity for anti-nuclear antibodies, anti-dsDNA, and HbA1c levels between the two groups, these differences were not statistically significant.

Disscussion

This study highlights the need for close monitoring of long COVID development in patients with elevated anti-TPO titers, which can be indicated by strongly elevated SARS-CoV-2-specific T cell response and moderately raised anti-spike IgG levels even long after the acute infection. However, our results do not exclude the possibility of new-onset thyroid autoimmunity after COVID-19, and further investigations are required to clarify the etiological link between highly elevated anti-TPO titers and long COVID.

Mechanisms of long COVID and the path toward therapeutics

Long COVID, a type of post-acute sequelae of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) (PASC) defined by medically unexplained symptoms following infection with SARS-CoV-2, is a newly recognized infection-associated chronic condition that causes disability in some people. Substantial progress has been made in defining its epidemiology, biology, and pathophysiology. However, there is no cure for the tens of millions of people believed to be experiencing long COVID, and industry engagement in developing therapeutics has been limited. Here, we review the current state of knowledge regarding the biology and pathophysiology of long COVID, focusing on how the proposed mechanisms explain the physiology of the syndrome and how they provide a rationale for the implementation of a broad experimental medicine and clinical trials agenda. Progress toward preventing and curing long COVID and other infection-associated chronic conditions will require deep and sustained investment by funders and industry.

Understanding autoimmune response after SARS-CoV-2 infection and the pathogenesis/mechanisms of long COVID

COVID-19 posed a major challenge to the healthcare system and resources worldwide. The popularization of vaccines and the adoption of numerous prevention and control measures enabled the gradual end of the COVID-19 pandemic. However, successive occurrence of autoimmune diseases in patients with COVID-19 cannot be overlooked. Long COVID has been the major focus of research due to the long duration of different symptoms and the variety of systems involved. Autoimmunity may play a crucial role in the pathogenesis of long COVID. Here, we reviewed several autoimmune disorders occurring after COVID-19 infection and the pathogenesis of long COVID.

Exploring the role of galectin-9 and artemin as biomarkers in long COVID with chronic fatigue syndrome: links to inflammation and cognitive function

This study aimed to assess plasma galectin-9 (Gal-9) and artemin (ARTN) concentrations as potential biomarkers to differentiate individuals with Long COVID (LC) patients with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) from SARS-CoV-2 recovered (R) and healthy controls (HCs). Receiver operating characteristic (ROC) curve analysis determined a cut-off value of plasma Gal-9 and ARTN to differentiate LC patients from the R group and HCs in two independent cohorts. Positive correlations were observed between elevated plasma Gal-9 levels and inflammatory markers (e.g. SAA and IP-10), as well as sCD14 and I-FABP in LC patients. Gal-9 also exhibited a positive correlation with cognitive failure scores, suggesting its potential role in cognitive impairment in LC patients with ME/CFS. This study highlights plasma Gal-9 and/or ARTN as sensitive screening biomarkers for discriminating LC patients from controls. Notably, the elevation of LPS-binding protein in LC patients, as has been observed in HIV infected individuals, suggests microbial translocation. However, despite elevated Gal-9, we found a significant decline in ARTN levels in the plasma of people living with HIV (PLWH). Our study provides a novel and important role for Gal-9/ARTN in LC pathogenesis.

Gastrointestinal Sequelae of COVID-19: Investigating Post-Infection Complications-A Systematic Review

Gastrointestinal (GI) complications are significant manifestations of COVID-19 and are increasingly being recognized. These complications range from severe acute pancreatitis to colitis, adding complexity to diagnosis and management. A comprehensive database search was conducted using several databases. Our inclusion criteria encompassed studies reporting severe and long-term GI complications of COVID-19. Digestive disorders were categorized into infections, inflammatory conditions, vascular disorders, structural abnormalities, other diagnoses, and undiagnosed conditions. Of the 73 studies that were selected for full-text review, only 24 met our inclusion criteria. The study highlights a broad range of gastrointestinal complications following COVID-19 infection (excluding liver complications, which are examined separately), including inflammatory conditions, such as ulcerative colitis (UC), acute pancreatitis, and multisystem inflammatory syndrome in children (MIS-C). Other GI complications were reported such as vascular disorders, including diverse thrombotic events and structural abnormalities, which ranged from bowel perforations to adhesions. Additionally, undiagnosed conditions like nausea and abdominal pain were prevalent across different studies involving 561 patients. The findings emphasize the substantial impact of COVID-19 on the GI tract. Ongoing research and monitoring are crucial to understanding the long-term effects and developing effective management strategies for these complications.

Nirmatrelvir-Ritonavir and Symptoms in Adults With Postacute Sequelae of SARS-CoV-2 Infection: The STOP-PASC Randomized Clinical Trial

Importance

There is an urgent need to identify treatments for postacute sequelae of SARS-CoV-2 infection (PASC).

Objective

To assess the efficacy of a 15-day course of nirmatrelvir-ritonavir in reducing the severity of select PASC symptoms.

Design, Setting, and Participants

This was a 15-week blinded, placebo-controlled, randomized clinical trial conducted from November 2022 to September 2023 at Stanford University (California). The participants were adults with moderate to severe PASC symptoms of 3 months or longer duration.

Interventions

Participants were randomized 2:1 to treatment with oral nirmatrelvir-ritonavir (NMV/r, 300 mg and 100 mg) or with placebo-ritonavir (PBO/r) twice daily for 15 days.

Main Outcomes and Measures

Primary outcome was a pooled severity of 6 PASC symptoms (fatigue, brain fog, shortness of breath, body aches, gastrointestinal symptoms, and cardiovascular symptoms) based on a Likert scale score at 10 weeks. Secondary outcomes included symptom severity at different time points, symptom burden and relief, patient global measures, Patient-Reported Outcomes Measurement Information System (PROMIS) measures, orthostatic vital signs, and sit-to-stand test change from baseline.

Results

Of the 155 participants (median [IQR] age, 43 [34-54] years; 92 [59%] females), 102 were randomized to the NMV/r group and 53 to the PBO/r group. Nearly all participants (n = 153) had received the primary series for COVID-19 vaccination. Mean (SD) time between index SARS-CoV-2 infection and randomization was 17.5 (9.1) months. There was no statistically significant difference in the model-derived severity outcome pooled across the 6 core symptoms at 10 weeks between the NMV/r and PBO/r groups. No statistically significant between-group differences were found at 10 weeks in the Patient Global Impression of Severity or Patient Global Impression of Change scores, summative symptom scores, and change from baseline to 10 weeks in PROMIS fatigue, dyspnea, cognitive function, and physical function measures. Adverse event rates were similar in NMV/r and PBO/r groups and mostly of low grade.

Conclusions and Relevance

The results of this randomized clinical trial showed that a 15-day course of NMV/r in a population of patients with PASC was generally safe but did not demonstrate a significant benefit for improving select PASC symptoms in a mostly vaccinated cohort with protracted symptom duration. Further studies are needed to determine the role of antivirals in the treatment of PASC.

Trial Registration

ClinicalTrials.gov Identifier: NCT05576662.

Postacute Sequelae of COVID (PASC or Long COVID): An Evidenced-Based Approach

While the acute manifestations of infectious diseases are well known, in some individuals, symptoms can either persist or appear after the acute period. Postviral fatigue syndromes are recognized with other viral infections and are described after coronavirus disease 2019 (COVID-19). We have a growing number of individuals with symptoms that persist for weeks, months, and years. Here, we share the evidence regarding the abnormalities associated with postacute sequelae of COVID-19 (PASC) and therapeutics. We describe physiological and biochemical abnormalities seen in individuals reporting PASC. We describe the several evidence-based interventions to offer patients. It is expected that this growing understanding of the mechanisms driving PASC and the benefits seen with certain therapeutics may not only lead to better outcomes for those with PASC but may also have the potential for understanding and treating other postinfectious sequelae.

Differential decline of SARS-CoV-2-specific antibody levels, innate and adaptive immune cells, and shift of Th1/inflammatory to Th2 serum cytokine levels long after first COVID-19

BACKGROUND

SARS-CoV-2 has triggered a pandemic and contributes to long-lasting morbidity. Several studies have investigated immediate cellular and humoral immune responses during acute infection. However, little is known about long-term effects of COVID-19 on the immune system.

METHODS

We performed a longitudinal investigation of cellular and humoral immune parameters in 106 non-vaccinated subjects ten weeks (10 w) and ten months (10 m) after their first SARS-CoV-2 infection. Peripheral blood immune cells were analyzed by multiparametric flow cytometry, serum cytokines were examined by multiplex technology. Antibodies specific for the Spike protein (S), the receptor-binding domain (RBD) and the nucleocapsid protein (NC) were determined. All parameters measured 10 w and 10 m after infection were compared with those of a matched, noninfected control group (n = 98).

RESULTS

Whole blood flow cytometric analyses revealed that 10 m after COVID-19, convalescent patients compared to controls had reduced absolute granulocyte, monocyte, and lymphocyte counts, involving T, B, and NK cells, in particular CD3+CD45RA+CD62L+CD31+ recent thymic emigrant T cells and non-class-switched CD19+IgD+CD27+ memory B cells. Cellular changes were associated with a reversal from Th1- to Th2-dominated serum cytokine patterns. Strong declines of NC- and S-specific antibody levels were associated with younger age (by 10.3 years, p < .01) and fewer CD3-CD56+ NK and CD19+CD27+ B memory cells. Changes of T-cell subsets at 10 m such as normalization of effector and Treg numbers, decline of RTE, and increase of central memory T cell numbers were independent of antibody decline pattern.

CONCLUSIONS

COVID-19 causes long-term reduction of innate and adaptive immune cells which is associated with a Th2 serum cytokine profile. This may provide an immunological mechanism for long-term sequelae after COVID-19.

Post-Acute Sequelae and Mitochondrial Aberration in SARS-CoV-2 Infection

This review investigates links between post-acute sequelae of SARS-CoV-2 infection (PASC), post-infection viral persistence, mitochondrial involvement and aberrant innate immune response and cellular metabolism during SARS-CoV-2 infection. Advancement of proteomic and metabolomic studies now allows deeper investigation of alterations to cellular metabolism, autophagic processes and mitochondrial dysfunction caused by SARS-CoV-2 infection, while computational biology and machine learning have advanced methodologies of predicting virus-host gene and protein interactions. Particular focus is given to the interaction between viral genes and proteins with mitochondrial function and that of the innate immune system. Finally, the authors hypothesise that viral persistence may be a function of mitochondrial involvement in the sequestration of viral genetic material. While further work is necessary to understand the mechanisms definitively, a number of studies now point to the resolution of questions regarding the pathogenesis of PASC.

Non-human primate model of long-COVID identifies immune associates of hyperglycemia

Hyperglycemia, and exacerbation of pre-existing deficits in glucose metabolism, are manifestations of the post-acute sequelae of SARS-CoV-2. Our understanding of metabolic decline after acute COVID-19 remains unclear due to the lack of animal models. Here, we report a non-human primate model of metabolic post-acute sequelae of SARS-CoV-2 using SARS-CoV-2 infected African green monkeys. Using this model, we identify a dysregulated blood chemokine signature during acute COVID-19 that correlates with elevated and persistent hyperglycemia four months post-infection. Hyperglycemia also correlates with liver glycogen levels, but there is no evidence of substantial long-term SARS-CoV-2 replication in the liver and pancreas. Finally, we report a favorable glycemic effect of the SARS-CoV-2 mRNA vaccine, administered on day 4 post-infection. Together, these data suggest that the African green monkey model exhibits important similarities to humans and can be utilized to assess therapeutic candidates to combat COVID-related metabolic defects.

Plate-Based High-Throughput Fluorescence Assay for Assessing Enveloped Virus Integrity

Viruses are a considerable threat to global health and place major burdens on economies worldwide. Manufactured viruses are also being widely used as delivery agents to treat (gene therapies) or prevent diseases (vaccines). Therefore, it is vital to study and fully understand the infectious state of viruses. Current techniques used to study viruses are often slow or nonexistent, making the development of new techniques of paramount importance. Here we present a high-throughput and robust, cell-free plate-based assay (FAIRY: Fluorescence Assay for vIRal IntegritY), capable of differentiating intact from nonintact enveloped viruses, i.e, infectious from noninfectious. Using a thiazole orange-terminated polymer, a 99% increase in fluorescence was observed between treated (heat or virucide) and nontreated. The FAIRY assay allowed for the rapid determination of the infectivity of a range of enveloped viruses, highlighting its potential as a valuable tool for the study of viruses and interventions against them.

Vaccine and antiviral drug promise for preventing post-acute sequelae of COVID-19, and their combination for its treatment

Introduction

Most healthy individuals recover from acute SARS-CoV-2 infection, whereas a remarkable number continues to suffer from unexplained symptoms, known as Long COVID or post-acute COVID-19 syndrome (PACS). It is therefore imperative that methods for preventing and treating the onset of PASC be investigated with the utmost urgency.

Methods

A mathematical model of the immune response to vaccination and viral infection with SARS-CoV-2, incorporating immune memory cells, was developed.

Results and discussion

Similar to our previous model, persistent infection was observed by the residual virus in the host, implying the possibility of chronic inflammation and delayed recovery from tissue injury. Pre-infectious vaccination and antiviral medication administered during onset can reduce the acute viral load; however, they show no beneficial effects in preventing persistent infection. Therefore, the impact of these treatments on the PASC, which has been clinically observed, is mainly attributed to their role in preventing severe tissue damage caused by acute viral infections. For PASC patients with persistent infection, vaccination was observed to cause an immediate rapid increase in viral load, followed by a temporary decrease over approximately one year. The former was effectively suppressed by the coadministration of antiviral medications, indicating that this combination is a promising treatment for PASC.

Mechanisms of Gut-Related Viral Persistence in Long COVID

Long COVID (post-acute sequelae of COVID-19-PASC) is a consequence of infection by SARS-CoV-2 that continues to disrupt the well-being of millions of affected individuals for many months beyond their first infection. While the exact mechanisms underlying PASC remain to be defined, hypotheses regarding the pathogenesis of long COVID are varied and include (but are not limited to) dysregulated local or systemic inflammatory responses, autoimmune mechanisms, viral-induced hormonal imbalances, skeletal muscle abnormalities, complement dysregulation, novel abzymes, and long-term persistence of virus and/or fragments of viral RNA or proteins. This review article is based on a comprehensive review of the wide range of symptoms most often observed in long COVID and an attempt to integrate that information into a plausible hypothesis for the pathogenesis of PASC. In particular, it is proposed that long-term dysregulation of the gut in response to viral persistence could lead to the myriad of symptoms observed in PASC.

Large-scale genetic correlation studies explore the causal relationship and potential mechanism between gut microbiota and COVID-19-associated risks

Recent observational studies suggest that gut microorganisms are involved in the onset and development of coronavirus disease 2019 (COVID-19), but the potential causal relationship behind them remains unclear. Exposure data were derived from the MiBioGen consortium, encompassing 211 gut microbiota (n = 18,340). The outcome data were sourced from the COVID-19 host genetics initiative (round 7), including COVID-19 severity (n = 1,086,211), hospitalization (n = 2,095,324), and susceptibility (n = 2,597,856). First, a two-sample Mendelian randomization (TSMR) was performed to investigate the causal effect between gut microbiota and COVID-19 outcomes. Second, a two-step MR was used to explore the potential mediators and underlying mechanisms. Third, several sensitivity analyses were performed to verify the robustness of the results. Five gut microbes were found to have a potential causality with COVID-19 severity, namely Betaproteobacteria (beta = 0.096, p = 0.034), Christensenellaceae (beta = -0.092, p = 0.023), Adlercreutzia (beta = 0.072, p = 0.048), Coprococcus 1 (beta = 0.089, p = 0.032), Eisenbergiella (beta = 0.064, p = 0.024). Seven gut microbes were found to have a potential causality with COVID-19 hospitalization, namely Victivallaceae (beta = 0.037, p = 0.028), Actinomyces (beta = 0.047, p = 0.046), Coprococcus 2 (beta = -0.061, p = 0.031), Dorea (beta = 0.067, p = 0.016), Peptococcus (beta = -0.035, p = 0.049), Rikenellaceae RC9 gut group (beta = 0.034, p = 0.018), and Proteobacteria (beta = -0.069, p = 0.035). Two gut microbes were found to have a potential causality with COVID-19 susceptibility, namely Holdemanella (beta = -0.024, p = 0.023) and Lachnospiraceae FCS020 group (beta = 0.026, p = 0.027). Multi-omics mediation analyses indicate that numerous plasma proteins, metabolites, and immune factors are critical mediators linking gut microbiota with COVID-19 outcomes. Sensitivity analysis suggested no significant heterogeneity or pleiotropy. These findings revealed the causal correlation and potential mechanism between gut microbiota and COVID-19 outcomes, which may improve our understanding of the gut-lung axis in the etiology and pathology of COVID-19 in the future.

Unraveling the enigma of long COVID: novel aspects in pathogenesis, diagnosis, and treatment protocols

Long COVID, now unmistakably identified as a syndromic entity encompassing a complex spectrum of symptoms, demands immediate resolution of its elusive pathogenic underpinnings. The intricate interplay of diverse factors presents a complex puzzle, difficult to resolve, and thus poses a substantial challenge. As instances of long COVID manifest by repeated infections of SARS-CoV-2 and genetic predisposition, a detailed understanding in this regard is needed. This endeavor is a comprehensive exploration and analysis of the cascading pathogenetic events driven by viral persistence and replication. Beyond its morbidity, long COVID, more disabling than fatal, exacts one of the most substantial tolls on public health in contemporary times, with the potential to cripple national economies. The paper introduces a unified theory of long COVID, detailing a novel pathophysiological framework that interlinks persistent SARS-CoV-2 infection, autoimmunity, and systemic vascular pathology. We posit a model where viral reservoirs, immune dysregulation, and genetic predispositions converge to perpetuate disease. It challenges prevailing hypotheses with new evidence, suggesting innovative diagnostic and therapeutic approaches. The paper aims to shift the paradigm in long COVID research by providing an integrative perspective that encapsulates the multifaceted nature of the condition. We explain the immunological mechanisms, hypercoagulability states, and viral reservoirs in the skull that feed NeuroCOVID in patients with long COVID. Also, this study hints toward a patient approach and how to prioritize treatment sequences in long COVID patients in hospitals and clinics.

The persistence of SARS-CoV-2 in tissues and its association with long COVID symptoms: a cross-sectional cohort study in China

BACKGROUND

Growing evidence suggests that symptoms associated with post-COVID-19 condition (also known as long COVID) can affect multiple organs and systems in the human body, but their association with viral persistence is not clear. The aim of this study was to investigate the persistence of SARS-CoV-2 in diverse tissues at three timepoints following recovery from mild COVID-19, as well as its association with long COVID symptoms.

METHODS

This single-centre, cross-sectional cohort study was done at China-Japan Friendship Hospital in Beijing, China, following the omicron wave of COVID-19 in December, 2022. Individuals with mild COVID-19 confirmed by PCR or a lateral flow test scheduled to undergo gastroscopy, surgery, or chemotherapy, or scheduled for treatment in hospital for other reasons, at 1 month, 2 months, or 4 months after infection were enrolled in this study. Residual surgical samples, gastroscopy samples, and blood samples were collected approximately 1 month (18-33 days), 2 months (55-84 days), or 4 months (115-134 days) after infection. SARS-CoV-2 was detected by digital droplet PCR and further confirmed through RNA in-situ hybridisation, immunofluorescence, and immunohistochemistry. Telephone follow-up was done at 4 months post-infection to assess the association between the persistence of SARS-CoV-2 RNA and long COVID symptoms.

FINDINGS

Between Jan 3 and April 28, 2023, 317 tissue samples were collected from 225 patients, including 201 residual surgical specimens, 59 gastroscopy samples, and 57 blood component samples. Viral RNA was detected in 16 (30%) of 53 solid tissue samples collected at 1 month, 38 (27%) of 141 collected at 2 months, and seven (11%) of 66 collected at 4 months. Viral RNA was distributed across ten different types of solid tissues, including liver, kidney, stomach, intestine, brain, blood vessel, lung, breast, skin, and thyroid. Additionally, subgenomic RNA was detected in 26 (43%) of 61 solid tissue samples tested for subgenomic RNA that also tested positive for viral RNA. At 2 months after infection, viral RNA was detected in the plasma of three (33%), granulocytes of one (11%), and peripheral blood mononuclear cells of two (22%) of nine patients who were immunocompromised, but in none of these blood compartments in ten patients who were immunocompetent. Among 213 patients who completed the telephone questionnaire, 72 (34%) reported at least one long COVID symptom, with fatigue (21%, 44 of 213) being the most frequent symptom. Detection of viral RNA in recovered patients was significantly associated with the development of long COVID symptoms (odds ratio 5·17, 95% CI 2·64-10·13, p<0·0001). Patients with higher virus copy numbers had a higher likelihood of developing long COVID symptoms.

INTERPRETATION

Our findings suggest that residual SARS-CoV-2 can persist in patients who have recovered from mild COVID-19 and that there is a significant association between viral persistence and long COVID symptoms. Further research is needed to verify a mechanistic link and identify potential targets to improve long COVID symptoms.

FUNDING

National Natural Science Foundation of China, National Key R&D Program of China, Chinese Academy of Medical Sciences Innovation Fund for Medical Sciences, and New Cornerstone Science Foundation.

TRANSLATION

For the Chinese translation of the abstract see Supplementary Materials section.

Humoral anti-SARS-CoV-2 response in patients with different long COVID phenotypes

Long COVID (LC) is characterized by persistent symptoms following SARS-CoV-2 infection, with various mechanisms offered to explain its pathogenesis. This study explored whether adaptive humoral anti-SARS-CoV-2 responses differ in LC. Unvaccinated COVID-19 convalescents (n = 200) were enrolled, with 21.5% (n = 43) presenting LC three months post-infection. LC diagnosis was based on persistent symptom(s) and alterations in biochemical/clinical markers; three phenotypes were distinguished: cardiological, pulmonary, and psychiatric LC. All three phenotypes were characterized by significantly decreased seroprevalence of IgG antibodies against nucleocapsid (anti-NP). LC was associated with decreased odds of testing positive for anti-NP (OR = 0.35, 95%CI: 0.16-0.78, p = 0.001). Seropositive LC patients had lower anti-S1 and anti-S2 levels than individuals without LC, and those with pulmonary and psychological phenotypes also revealed decreased anti-RBD concentrations. The results indicate that LC can be characterized by diminished humoral response to SARS-CoV-2. The potential implication of this phenomenon in post-acute viral sequelae is discussed.

Autoimmune Sequelae After Delta or Omicron Variant SARS-CoV-2 Infection in a Highly Vaccinated Cohort

Importance

Studies have reported increased risk of autoimmune sequelae after SARS-CoV-2 infection. However, risk may potentially be attenuated by milder Omicron (B.1.1.529) variant infection and availability of booster vaccination.

Objective

To estimate the 300-day risk of new-incident autoimmune sequelae after SARS-CoV-2 Delta or Omicron BA.1 or BA.2 variant infection in adults who received COVID-19 vaccines and boosters, compared with a contemporary control group without infection.

Design, Setting, and Participants

This cohort study in Singapore enrolled adults from September 1, 2021, to March 7, 2022, and followed up for 300 days. Participants were adults aged 18 years or older with SARS-CoV-2 infection during the predominance of the Delta and Omicron BA.1 or BA.2 variants and were still alive at 30 days after COVID-19 diagnosis.

Exposure

The national SARS-CoV-2 testing registry was used to construct cohorts of adults with SARS-CoV-2 Delta or Omicron BA.1 or BA.2 variant infection (hereafter, cases) and a contemporaneous group with negative polymerase chain reaction or rapid antigen test results (hereafter, controls).

Main Outcomes and Measures

New-incident autoimmune diagnoses after SARS-CoV-2 infection. This information was recorded in the MediClaims national health care claims database and identified 31 to 300 days after index date of infection. Risks and excess burdens were estimated using Cox proportional hazards regression model with overlap weights applied.

Results

In total, 1 766 036 adults (915 096 females [51.9%]; mean [SD] age, 49 [18] years) were included in the study population, with 480 082 (27.2%) categorized as cases and 1 285 954 (72.8%) as controls. Of these adults, 73.1% had Chinese, 13.7% Malay, and 9.9% Indian ethnicity. There were 104 179 cases and 666 575 controls included during the Delta variant-predominance transmission, while 375 903 cases and 619 379 controls were included during the Omicron variant-predominance transmission. During the Delta variant period, 81.1% of cases had completed primary vaccination; during the Omicron variant period, 74.6% of cases received boosters. No significantly elevated risk of 12 prespecified autoimmune sequelae was recorded across the Omicron and Delta variant cohorts. Elevated risks of inflammatory bowel disease (adjusted hazard ratio [AHR], 2.23; 95% CI, 1.45-3.46; P < .001) and bullous skin disorders (AHR, 4.88; 95% CI, 2.47-9.66; P < .001) were observed only in the subset of COVID-19 cases requiring hospitalization during the predominance of the Omicron variant. While elevated risk of vasculitis (AHR, 5.74; 95% CI, 1.48-22.23; P = .01) was observed in vaccine-breakthrough Omicron variant infections, no increased risk of vasculitis was observed in the corresponding subgroup who received boosters.

Conclusions and Relevance

This cohort study observed no significantly elevated long-term risk of autoimmune sequelae after SARS-CoV-2 Delta and Omicron BA.1 or BA.2 variant infection, except for a modestly increased risk of inflammatory bowel disease and bullous skin disorders in the hospitalized subgroup during the predominance of the Omicron variant. Booster vaccination appeared to mitigate the risk of long-term autoimmune sequelae.