Background: Long COVID, or post-COVID-19 condition (PCC), affects around 36% of individuals following SARS-CoV-2 infection, manifesting as persistent fatigue, cognitive dysfunction, and dysautonomia among its hallmark features. Affecting an estimated 400 million individuals globally, it imposes an annual economic burden exceeding $1 trillion, yet no pharmacological therapy has demonstrated consistent efficacy in adequately powered randomized controlled trials. Transcutaneous auricular vagus nerve stimulation (taVNS) has emerged as a candidate intervention targeting the autonomic dysfunction and neuroinflammation responsible for PCC pathophysiology. Methods: We conducted a PRISMA 2020-compliant systematic review (PROSPERO: CRD420261287286) searching PubMed, Scopus, Cochrane, and Web of Science databases from inception to January 2026 for studies evaluating any form of VNS in adults with Long COVID. Risk of bias was assessed using the Cochrane Risk of Bias 2 (RoB 2) tool, the JADAD scale, and the PEDro scale. Certainty of evidence was evaluated using the GRADE framework. Narrative synthesis followed SWiM guidelines. Results: Five studies (n = 154 participants) (three randomized controlled trials (RCTs) and two single-arm studies) met inclusion criteria. Three of five studies (60%) were rated high overall risk of bias; only two RCTs achieved “some concerns.” The only adequately double-blinded RCT found no significant between-group differences across all outcomes. Paradoxically, in the best-powered RCT (Percin et al.), sham stimulation produced significantly greater fatigue improvement than active taVNS, despite active taVNS producing significant HRV increases consistent with cardiac autonomic modulation. All efficacy outcomes were rated “very low” certainty (GRADE); safety was rated “low” certainty. Conclusions: Currently available evidence supporting the use of taVNS for Long COVID remains limited, and the absence of reliable target engagement markers in the included studies constrains confidence in this approach. Nonetheless, the physiological rationale remains sound, and the favorable safety profile across all included studies supports the feasibility of future investigation. However, given that positive findings were confined to inadequately controlled studies, enthusiasm for further research should be directed first toward mechanistic clarification and rigorous dose-finding work. Large-scale, double-blind, sham-controlled trials incorporating validated markers of vagal engagement are required before taVNS can be firmly recommended for COVID-19 sequelae management.

Background and Objectives: Coronavirus disease 2019 (COVID-19) is characterized by excessive inflammatory responses, including the so-called cytokine storm, which contributes substantially to morbidity and mortality in hospitalized patients. The vagus nerve, through the cholinergic anti-inflammatory pathway, represents a theoretically attractive therapeutic target for modulating systemic inflammation. Vagus nerve stimulation (VNS) has emerged as a potential adjunctive treatment for COVID-19, with several randomized controlled trials (RCTs) investigating its efficacy on inflammatory biomarkers and clinical outcomes. The quality of this evidence base has not been rigorously evaluated. This systematic review critically appraises all available RCT evidence for VNS in hospitalized COVID-19 patients. Materials and Methods: We systematically searched PubMed, Scopus, Cochrane (CENTRAL), and Web of Science from database inception to January 2026, for RCTs evaluating any form of VNS (invasive, non-invasive, cervical, or auricular) in hospitalized patients with confirmed acute COVID-19. Two reviewers independently screened titles, abstracts, and full texts according to pre-specified eligibility criteria. Risk of bias was assessed using the Cochrane Risk of Bias 2 (RoB 2) tool, with assessments initially performed using multiple artificial intelligence tools and subsequently validated by the authors in accordance with PRISMA 2020 guidelines. Given substantial heterogeneity and high risk of bias, narrative synthesis was performed rather than meta-analysis. Also, GRADE assessment was performed. Results: From 437 records identified, six RCTs comprising 221 patients met the inclusion criteria. Five trials (83%) were rated as high risk of bias, primarily due to inadequate blinding, substantial baseline imbalances, significant missing data and extensive multiple testing without statistical correction. The single double-blind trial with a credible sham control (Rangon et al.) found null results across all outcomes, including clinical progression, ICU transfer, and mortality, while the five “high” risk-of-bias trials generally reported positive findings on various inflammatory markers and clinical outcomes. One trial (Corrêa et al.) measured heart rate variability as a direct indicator of vagal activation and found no change despite claiming anti-inflammatory effects, contradicting the proposed mechanism of action. Significant cognitive findings from an interim analysis (Uehara et al., n = 21) disappeared in the larger completed trial (Corrêa et al., n = 52), providing empirical demonstration of false positive findings in small, underpowered studies. Conclusions: Currently available evidence supporting the use of VNS for acute COVID-19 remains scarce; however, the physiological rationale remains sound, although the absence of reliable target engagement markers in the included studies limits confidence in this treatment method. Large-scale, double-blind, sham-controlled trials are required before VNS can be firmly recommended for COVID-19 management.