The effect of vaccination on foot and mouth disease virus transmission among dairy cows.

The aim of this study was to quantify the effect of a single vaccination of dairy cows on foot and mouth disease virus (FMDV) transmission. To estimate if vaccination could significantly reduce virus transmission, we performed two replicates of a transmission experiment with one group of vaccinated and one group of non-vaccinated dairy cows (ten animals per group). Half of both groups were intranasally inoculated, with FMDV field isolate O/NET2001, and housed with the other half of the group (contact-exposed cows) from the next day onwards. Virus transmission was quantified by estimating the reproduction ratio R, which is the average number of secondary cases caused by one infectious animal. In the non-vaccinated groups all cows became infected and Rnv was significantly above 1. In the vaccinated groups infection was demonstrated in three inoculated cows, and no transmission was observed (Rv was 0, not significantly below 1). Transmission was significantly reduced in the groups of vaccinated cows when compared to the groups of unvaccinated cows. Our findings indicate that after a single vaccination cows are protected against infection of FMD and that most likely no virus transmission will occur within a vaccinated herd.