Expression of SARS-CoV-2 spike protein in cerebral Arteries: Implications for hemorrhagic stroke Post-mRNA vaccination

Background: The rapid deployment of mRNA vaccines for SARS-CoV-2, such as BNT162b2 (BioNTech-Pfizer) and mRNA-1273 (Moderna), provided a critical tool in combating the COVID-19 pandemic. While their short-term safety and efficacy were demonstrated in clinical trials, rare adverse events, including hemorrhagic strokes, have been reported after widespread use. However, the long-term biodistribution and effects of mRNA vaccines remain underexplored. This study aimed to investigate the long-term presence of SARS-CoV-2 spike protein in brain tissues of patients with hemorrhagic strokes, examining its potential association with mRNA vaccination. Methods: A total of 19 cases of hemorrhagic stroke from 2023 to 2024 were retrospectively analyzed. Immunohistochemical staining for SARS-CoV-2 spike protein and nucleocapsid protein was performed on tissue samples. In situ hybridization was conducted in selected cases to confirm the origin of spike protein expression (vaccine or viral infection). Vaccination history and SARS-CoV-2 infection status were documented for all cases. Results: Spike protein expression was detected in 43.8 % of vaccinated patients, predominantly localized to the intima of cerebral arteries, even up to 17 months post-vaccination. While no active inflammatory changes were identified, infiltration of CD4-, CD8- and CD68- positive cells was observed in the spike protein positive vessels. In situ hybridization confirmed the presence of both vaccine-derived mRNA and SARS-CoV-2 virus-derived mRNA, which encode the spike protein, in select cases. Notably, spike protein positivity was observed exclusively in female patients (P = 0.015). None of the cases showed nucleocapsid protein positivity, supporting the absence of active viral infection. Conclusion: Although the possibility of spike protein expression due to asymptomatic SARS-CoV-2 infection cannot be entirely excluded, this study demonstrated prolonged presence of SARS-CoV-2 spike protein in the cerebral arteries following mRNA vaccination. Additionally, some inflammatory cell infiltration was observed in spike-positive vessels. These findings raise significant concerns regarding the biodistribution of lipid nanoparticle-based vaccines and their long-term safety. Global replication studies are urgently required to validate these findings and ensure comprehensive safety evaluations of mRNA vaccines.