FOOT-AND-MOUTH-DISEASE - CHALLENGE OF CATTLE AFTER MULTIPLE VACCINATIONS

Four groups of six cattle were vaccinated from two to five times at 6 month intervals with two different trivalent FMD vaccines licensed in the given year. The FMDV type A strains in the vaccines designated A5F and A5B were closely related. Three months after the last vaccination the cattle were challenged by contact with animals inoculated with th e original field strain A5B, The inoculated animals developed typical FMD symptoms with vesicles in the mouth and on the feet. Those cattle which had received vaccines that did not contain strain A5B also becam e severely sick, even after five vaccinations. Animals vaccinated twic e with type B containing vaccine were also not completely protected. A safe protection can obviously only be achieved for fairly short perio ds of time if vaccine and challenge strain are homologous. It is propo sed to change the rules of licensing, to speed up the procedure to vac cinate in cases of outbreaks. The need for further research, especiall y into improving vaccines, is stressed.