Brucella abortus (strain 19) vaccine: potency tests in cattle

Abstract

A potency test in cattle compared the immunogenicity of S19 vaccine produced by the routine continuous culture process used at the CVL Weybridge with a Standard S19 vaccine produced on potato agar. The two vaccines conferred equal degrees of protection against virulent Brucella abortus (strain 544). The challenge organism caused a generalized infection in seven out of 11 unvaccinated controls but in only one out of the 11 animals vaccinated with the production batch of S19 and in none out of the 12 animals vaccinated with the Standard S19 vaccine. The S19 vaccines, inoculated into 5-month-old calves, gave rise to serological responses which, as measured by the serum agglutination, complement fixation and Rose Bengal plate tests had virtually disappeared 28 weeks after vaccination. The response as measured by the antiglobulin test lasted longer but had disappeared in most of the animals by the time they were challenged, 38 weeks after vaccination. These results confirm previous findings that strain 19 vaccine confers a worthwhile degree of protection against Br. abortus infection.