Clinical outcomes and virology of equine influenza in a naïve population and in horses infected soon after receiving one dose of vaccine.

As part of the control measures of the equine influenza (EI) outbreak, in addition to the strategic use of vaccination to provide buffer zones around infected populations, approval was obtained to vaccinate Thoroughbred racing horses. We review the clinical expression of the disease and virus excretion in a population of racehorses that were exposed to EI approximately 7 days after administration of a single dose of the canarypox-vectored recombinant compared with a similar unvaccinated population of horses at a nearby racetrack. Although this study was undertaken opportunistically and under the difficult field conditions that prevailed during the outbreak, our observations demonstrate that an appropriate vaccine can be effectively used as a disease control measure, even in the face of an outbreak, and therefore should be rapidly implemented as soon as there is evidence of infection in a naïve population.