Further evaluation of higher potency vaccines for early protection of cattle against FMDV direct contact challenge.

The effect of administering higher payload FMD vaccines 10 days prior to severe direct contact challenge on protection from clinical disease and sub-clinical infection was investigated in cattle using two antigen payloads (single strength and 10-fold). Regardless of antigen payload, vaccination was shown to significantly reduce the number of clinically infected animals, and significantly reduce virus excretion shortly after challenge, when compared with the unvaccinated group (P<0.05). Although FMDV transmission occurred from single strength vaccinated infected cattle to similarly vaccinated cattle held in indirect contact, no disease was induced in these animals. These studies further confirm that emergency vaccination does significantly reduce clinical disease and sub-clinical virus replication and excretion, particularly early post exposure, thereby reducing the possibility of transmission between animals and herds. To be most effective, however, the results also substantiate that time of vaccination prior to challenge significantly influences the number of animals becoming infected, so the decision to vaccinate should be made swiftly, to allow maximum opportunity for protective immunity to develop.