Publication of positive preclinical study results evaluating its adenovirus-based oral mucosal vaccine platform against Highly Pathogenic Avian Influenza (HPAI) H5N1, a pathogenic virus that poses a significant threat to public health. The complete, peer-reviewed study results, which were published in Frontiers in Immunology, demonstrate that Vaxart’s second-generation vaccine candidate, VXA-H5-02, elicits both mucosal and systemic neutralizing antibody responses, offering comprehensive protection against lethal challenge with H5N1 clade 2.3.4.4b. The company previously reported topline study results in 2025.

Key Study Highlights

100% Survival Rate: All ferrets immunized with VXA-H5-02 survived a lethal challenge with H5N1 clade 2.3.4.4b, whereas 100% of unvaccinated control animals rapidly succumbed to infection by Day 6 post-challenge (p< 0.001).
Significant Viral Load & Shedding Reduction: VXA-H5-02 vaccination produced a ~2.3-log reduction in infectious viral shedding by Day 3 post-challenge compared to controls. By Day 6–7, viable virus was below the limit of detection in nasal wash samples, and 7 out of 8 animals completely cleared viral RNA by Day 8/9.
Mucosal & Cross-Neutralizing Immunity: Immunization with VXA-H5-02 elicited strong serum neutralizing titers and mucosal IgA/IgG responses in nasal wash fluid. Higher pre-challenge nasal IgA levels showed the strongest negative correlation with post-challenge viral shedding (r = -0.6059).
Cross-Clade Protection: Serum from VXA-H5-02 immunized animals demonstrated cross-neutralizing activity against divergent H5 strains, including the recently emerged H5N1 clade 2.3.2.1e. Additionally, the clade-mismatched first-generation vaccine (ND1.1, encoding clade 2.1.3.2) conferred 37% survival against the clade 2.3.4.4b challenge.