Figure 5.

Schematic representation of the vaccination and challenge protocol: One-to-two year-old horses of both sexes (n = 12) were randomly separated into group 1 (n = 6) and group 2 (n = 6) and inoculated by aerosol inhalation with a virus preparation containing 3 × 10⁸ FFU of clade 1 Ohio/03 LAIV and 3 × 10⁸ FFU of clade 2 Rich/07 LAIV using a prime-boost regimen. Individual rectal temperature and viral shedding were measured in each horse before and at days 2, 3, and 7 after each dose (safety). Twenty-eight days after the boost, samples were collected and presence of serum antibodies was assessed by HAI (immunogenicity). Fifty-seven days after prime, vaccinated (n = 12) and mock-vaccinated (n = 6) horses were randomly separated into group 1 and group 2 and challenged by aerosol inhalation with 5 × 10⁷ EID₅₀ of A/equine/Kentucky/2014 WT (KY/14 WT; n = 6 vaccinated group 1 and n = 3 mock-vaccinated) or 5 × 10⁷ EID₅₀ of Rich/07 WT (n = 6 vaccinated group 2 and n = 3 mock-vaccinated) to assess protection against clade 1 and 2 EIVs, respectively. Rectal temperatures and virus shedding were evaluated (protection efficacy) for eight days after challenge.