Equine influenza: patterns of disease and seroprevalence in Thoroughbred studs and implications for vaccination

This study included 10 large Thoroughbred horse studs in the upper Hunter Valley of New South Wales and in southeast Queensland, Australia. The aims were to describe the EI epidemic in studs in the Special Restricted Area (Purple Zone) of NSW, to estimate seroprevalence among different groups of horses on these studs and to look for evidence of exposure to EI virus in horses on 'vaccinated' studs in southeast Queensland that were thought to have remained free of infection. As serology results from Queensland suggest that vaccination may have reduced the sensitivity of clinical surveillance to detect the presence of infection on 'vaccinated' premises, we conclude that vaccine efficacy must be considered in terms of reduction in clinical disease, as well as in terms of infection and infectiousness.