Complete adherence to vaccination programmes is paramount for disease control. The fact that farmers and vets often do not follow recommended vaccination procedures might explain why vaccination has failed to reduce the overall BVD prevalence in the past four decades.
In one large survey in Pennsylvania, only 27% of BVDV vaccines were used correctly. In another study surveying 71 farms in 4 UK counties, just 24% of the farms completed the primary vaccination course at the recommended time. This would have profound effects on the efficacy of any vaccine.