Vaxart, Inc. (OTCQX: VXRT) announced the publication of preclinical study results for its oral H5N1 vaccine candidate, VXA-H5-02, in the peer-reviewed journal Frontiers in Immunology. The study, conducted in ferrets, showed 100% survival following exposure to a lethal dose of H5N1 clade 2.3.4.4b virus.

All unvaccinated control animals died by day six post-challenge, while all ferrets immunized with VXA-H5-02 survived. The vaccine also produced approximately a 2.3-log reduction in infectious viral shedding by day three post-challenge compared to controls. By days six to seven, viable virus fell below the limit of detection in nasal wash samples, and seven of eight animals cleared viral RNA by days eight to nine.

The study found that VXA-H5-02 elicited both mucosal and systemic neutralizing antibody responses. Higher pre-challenge nasal IgA levels showed the strongest negative correlation with post-challenge viral shedding. Serum from vaccinated animals also demonstrated cross-neutralizing activity against divergent H5 strains, including H5N1 clade 2.3.2.1e.

A clade-mismatched first-generation vaccine, encoding clade 2.1.3.2, conferred 37% survival against the clade 2.3.4.4b challenge, according to the study data.

The vaccine was delivered via non-replicating recombinant adenovirus type 5 vectors expressing viral hemagglutinin. Because ferrets cannot use tablets, a liquid formulation was administered directly to the small intestine via endoscopic delivery on days zero and 28 to simulate enteric-coated tablet release. Challenge occurred on day 56.

"The 100% survival rate following challenge with a lethal dose of virus underscores the robust immune protection our oral influenza vaccine candidates may be able to provide," said Dr. Sean Tucker, chief scientific officer of Vaxart. VXA-H5-02 has not been evaluated in humans and is not the subject of an investigational new drug application.