EMERGENCY VACCINATION AGAINST FOOT-AND-MOUTH-DISEASE - RATE OF DEVELOPMENT OF IMMUNITY AND ITS IMPLICATIONS FOR THE CARRIER STATE

Emergency foot-and-mouth disease (FMD) vaccines prepared from antigens held in the International Vaccine Bank at Pirbright were administered to cattle and pigs and the levels of protection were assessed followi ng challenge by contact with infected pigs. Both Al(OH)(3)/saponin and oil-based cattle vaccines proved to be extremely effective and protec ted soon after vaccination (4 days postvaccination), whereas the pigs were seldom protected before 21 and 28 days postvaccination, probably due to lower levels of antibody and overwhelming challenge conditions. Early production of cattle occurred in the absence of significant lev els of circulating antibody as measured by enzyme-linked immunosorbent assay, a neutralization assay and a passive protection test. A large number of the cattle vaccinated with the O-1 Lausanne strain of FMD an d subsequently challenged with this virus became persistently infected and there appeared to be a correlation with the time interval between vaccination and challenge. When the same cattle were vaccinated appro ximately 4 months later with a different strain of FMD, C-1 Oberbayern , and challenged with this strain, the number of persistently infected animals was considerably lower. The results are discussed in the cont ext of the use of emergency vaccines to prevent the dissemination of F MD from disease foci.