The relationship between the 140S antigen dose in aqueous foot-and-mouth disease vaccines and the serum antibody response of cattle.

Groups of eight or 12 cattle were injected with dilutions of aqueous saponized vaccines containing 329 760 to 7 ng of 140S O1BFS 1860 strain foot-and-mouth disease antigen per dose. Four months later the animals were subdivided into groups of four and revaccinated with vaccines containing 329 760, 9160 and 42 ng of antigen per dose. Responses were established by taking serum samples from the animals periodically and examining these for neutralizing antibody activity. The results showed that after primary vaccination the dose of antigen in vaccines influenced the earliest time of protection, the peak antibody titres attained and probably, the duration of immunity. At 21 days after vaccination the log antigen-antibody response slope was linear between 7 and 9, 160 ng, with an inclination of 0.53, indicating that every doubling of the vaccine antigen dose produced an increase of 0.16 log10SN50 in the mean serum antibody titre. The secondary response was influenced by the antigen dose in the second vaccination and to a lesser extent by that in the first vaccination also.