Serum samples were obtained from 281 heifers vaccinated with Brucella abortus strain 19, and from 50 heifers that had received two injections of killed B. abortus strain 45/20 adjuvant (K45/20A) vaccine. The serological response measured by the brucellosis radioimmunoassay (RIA) was compared with responses measured by other tests.
The serological responses of cattle during the first weeks after strain 19 vaccination were found to give little guide to the frequency of persistent reactions.
In the case of strain 19, persistent reactions were considered to be those occurring 12 or more months after vaccination. In heifers vaccinated at the recommended age, small numbers of persistent reactions were given by the RIA (four in 374 sera), the complement fixation test using warm fixation (CFTW) (six in 383) and cold fixation (one in 185), the serum agglutination test (two in 222) and the indirect haemolysis test (IHLT) (two in 369). The Rose Bengal plate test gave 74 persistent reactions in 374 sera.
Five of the 50 heifers gave particularly prolonged responses to K45/20A vaccine. In these animals the RIA and IHLT remained positive for longer than the CFTW.