Attempts to immunoprotect adult horses, specifically pregnant mares, with commercial vaccines against clinical disease induced by equine herpesvirus-1.

In a project lasting 4 years more than 300 Lipizzans, around 180 of them adults, were vaccinated systematically against Equine Herpesvirus-1 (EHV-1) and representative groups thereof were serologically controlled for their antibody responses. In part, vaccination intervals recommended on packing slips were followed, in part other intervals, implicated by intermediary results, were used. A live virus vaccine proved ineffective if humoral antibodies were present. An oil-adjuvanted vaccine proved of highest antiviral immunogenicity, but after repeated revaccinations caused severe local reactions so frequently that we had to discontinue its use in adults. Fetal calf serum originating from the cell cultures used for viral propagation and not eliminated from the marketed product, was accused of being responsible for the incompatibilities. An inactivated mixed virus vaccine was of weak antigenicity regarding its EHV-1 component (whereas good regarding the influenza viruses) so that it proved unsatisfactory for primary immunization. It was, however, potent enough, and clinically well tolerated, to maintain suitable antibody levels in horses which had been initially primed by the oil-adjuvanted vaccine. Consequently, optimal humoral immunity as well as clinical acceptability resulted when two different vaccines were used, one for induction, the other for maintenance of protection. Vaccination intervals different from those on the packing slips are recommended for the mixed vaccine.