Analysis of status of vaccination and development of fever in trotters in Sweden during an outbreak of influenza type A2 (H3N8)

An outbreak of influenza type A2 affecting a population of 603 vaccinated trotters in three different trotting tracks in Sweden during the spring of 1990 was investigated using logistic regression. The analyses were performed with data from the entire population and with data from a subpopulation consisting of 150 horses which had been vaccinated solely with Isovac Flu vet, and who had had at least four such vaccinations. The results from analysis of the entire population showed differences between tracks, and lower risk for geldings and for horses 4 years or older. The risk of developing clinical signs was increased for horses vaccinated more than 119 days before the outbreak. The results from analysis of Iscovac Flu vet-vaccinated horses also showed differences between tracks, lower risk for geldings, and increased risk for horses vaccinated more than 119 days before the outbreak.