In vitrocomparison of foot-and-mouth disease virus subtype variants causing disease in vaccinated cattle

Abstract
Summary: Foot-and-mouth disease virus isolates of types O, A and SAT 2, from diseased animals in herds routinely vaccinated twice a year were compared antigenically with the vaccine strains in the complement-fixation, neutralization and radial immunodiffusion tests. It was found that strains which had readily infected vaccinated cattle hadRvalues against the vaccine strain in the complement- fixation and radial immunodiffusion tests of 30 or less, while strains causing primary outbreaks with little spread hadRvalues of 30–40. Threefold differences in humoral neutralizing antibody concentration between the field variant and the vaccine strain in sera from vaccinated animals were likely to be significant in terms of protection.