Field studies on equine influenza vaccination regimes in Thoroughbred foals and yearlings

The purpose of these studies was to examine the response of Thoroughbred fo als and yearlings to different influenza vaccines and vaccination regimes. The horses' antibody levels against haemagglutinin, an established correlat e of protection were measured by haemagglutination inhibition. The first st udy investigated the extent to which maternal antibodies interfered with th e humoral response to a subunit vaccine. The findings suggest that repeat v accination in the face of maternal antibodies may induce tolerance as defin ed by serological testing. The second study compared the immune response el icited by a subunit immune stimulating complex (ISCOM) vaccine, an inactiva ted whole virus vaccine and the same product containing equine herpesviruse s and equine reoviruses in addition to equine influenza virus. The monovale nt vaccine induced a significantly better response than the ISCOM or the mu ltivalent vaccine. The final study demonstrated that the inclusion of an ad ditional booster vaccination, between the second and third vaccination reco mmended by the vaccine manufacturers and required under the rules of racing in certain countries, is of benefit to young horses. Since these studies w ere performed, several of the vaccines have been updated with more recent v irus strains in line with WHO/OIE recommendations. However, the general pri nciples (C) 2001 Harcourt Publishers Ltd.