FAILURE OF VACCINATION TO PREVENT OUTBREAKS OF FOOT-AND-MOUTH-DISEASE

Outbreaks of foot-and-mouth disease persist in dairy cattle herds in S audi Arabia despite revaccination at intervals of 4-6 months, Vaccine trials provide data on antibody responses following vaccination. Using this information we developed a mathematical model of the decay of pr otective antibodies with which we estimated the fraction of susceptibl e animals at a given time after vaccination. The model describes the d ata well, suggesting over 95% take with an antibody half-life of 43 da ys, Farm records provided data on the time course of five outbreaks. W e applied a 'SLIR' epidemiological model to these data, fitting a sing le parameter representing disease transmission rate. The analysis prov ides estimates of the basic reproduction number, R(0), which may excee d 70 in some cases, We conclude that the critical intervaccination int erval which would provide herd immunity against FMDV is unrealisticall y short, especially for heterologous challenge. We suggest that it may not be possible to prevent foot-and-mouth disease outbreaks on these farms using currently available vaccines.