Studies with inactivated equine influenza vaccine: 2. Protection against experimental infection with influenza virus A/equine/Newmarket/79 (H3N8)

Abstract

Forty ponies immunized with inactivated virus vaccine containing A/equine/Miami/63 (H3N8) virus and six unvaccinated, seronegative ponies were experimentally challenged with a representative of recent equine H3N8 virus isolates, A/equine/Newmarket/79. All unvaccinated ponies became infected as judged by virus excretion, febrile responses and antibody responses, but only two of the vaccinated ponies were fully protected. Pre-challenge antibody levels to A/Newmarket/79 virus detected by single radial haemolysis (SRH) correlated well with the degree of clinical protection but the levels required for complete protection (SRH zones > 65 mm2) were high. The importance of these results in relation to conventional vaccination procedures against equine influenza is discussed.