Immune response to virus-infection-associated (VIA) antigen in cattle repeatedly vaccinated with foot-and-mouth disease virus inactivated by formalin or acetylethyleneimine.

The results of experiments to investigate antibody to 'virus infection associated' (VIA) antigen in cattle repeatedly vaccinated with formalin- or acetylethyleneimine- (AEI) inactivated foot-and-mouth disease (FMD) vaccines under laboratory conditions are reported. Results are also presented from some vaccinated animals subsequently exposed to FMD infection. Antibody against VIA was not detected before and after the first vaccination with formalin or AEI-inactivated vaccine but did develop in all animals after the second formalin vaccination and persisted throughout the experiment. After the second AEI vaccination, 4 of 12 animals developed antibody which persisted for at least 37 days. This transient response in some cattle was repeated after successive vaccinations but, in general, more animals responded as the number of vaccinations increased. After exposure to infection a transient VIA antibody response was occasionally observed in immune AEI-vaccinated animals. Some immune repeatedly AEI-vaccinated cattle did not develop detectable VIA antibody after challenge despite the persistence of virus in oesophageal-pharyngeal (O/P) fluid. The presence of antibody to VIA antigen is not conclusive proof that vaccinated animals have been exposed to infection and field data must be interpreted with caution.