Immunization with virus-like vesicle-based COVID-19 vaccine induces robust systemic and mucosal immunity

Coronavirus disease 2019 (COVID-19) has led to significant global morbidity and mortality. Although several vaccines are approved, developing more effective candidates remains essential for long-term prevention. In this study, we present a COVID-19 vaccine candidate using a virus-like vesicle (VLV) platform, an enveloped self-amplifying RNA replicon incorporating an evolved Semliki Forest virus RNA polymerase and VSV glycoprotein. Two constructs were generated: VLV-S-FL (full-length spike protein) and VLV-S-RBD (receptor-binding domain). In C57BL/6J mice, VLV-S-FL elicited robust anti-spike antibody and T cell responses, with antibody levels comparable to those induced by the BNT162b2 mRNA vaccine. Prime-boost immunization with VLV-S-FL provided in vivo protection against SARS-CoV-2. Notably, intranasal boosting enhanced mucosal immunity, including IgA production and recruitment of CD4+ T, CD8+ T, and B cells in BALF. These findings suggest that VLV-S-FL is a promising COVID-19 vaccine capable of inducing both systemic and mucosal immune responses to prevent infection and reduce disease severity.