A randomized field trial of live epizootic bovine abortion agent (EBAA) vaccine demonstrates safety and efficacy

Epizootic bovine abortion (EBA) is a devastating late-term abortion caused by Pajaroellobacter abortibovis that, until recently, could only be controlled through management practices. A live epizootic bovine abortion agent (EBAA) vaccine was developed and reported to be both safe and effective in controlled challenge studies. Here we examined vaccine performance with randomized and blinded study conducted under field conditions. The study was divided into phases: safety, breeding efficiency, early fetal loss, and efficacy. An equal number of heifers were inoculated with either placebo or EBAA vaccine, 95 days prior to breeding. No anaphylaxis was observed, and the only notable adverse reactions were mild swelling at the injection site. Heifer conception rates were higher in placebo controls compared to the vaccinates while placebo controls experienced a greater percentage of early fetal losses; neither were significant. Vaccine efficacy was measured by both calving outcomes and production of Pajaroellobacter abortibovis -specific antibody. EBAA vaccinated heifers produced a 10% higher calf crop as compared to controls, though the difference was not significant. Significant differences were found when comparing P. abortibovis -associated losses in vaccinates to controls. Ninety-eight percent of vaccinated heifers seroconverted following vaccination as compared to 0% in the placebo group. Concomitant administration of Brucella abortus Strain RB51 and Anavac® vaccines had little to no effect on EBAA vaccine efficacy. Taken together, data demonstrates vaccine safety and efficacy of EBAA vaccine PCN 1544.00 in the face of natural field exposure.