Estimation of efficacy of Startvac® vaccination in dairy herds

A large field trial was performed to estimate Startvac vaccine efficacy in two herds. The chosen study design of within herd randomization of vaccination allowed us the estimate vaccine efficacy within herd using a within herd randomization schedule. The farms showed a large difference in their ability to control infection during the study. For both farms, the prevalence of CNS remained more or less constant. Prevalence of S. aureus remained the same or slightly increased in farm 1 but dropped dramatically to a very low prevalence in herd 2. Vaccine effects were observed throughout all analyses that were performed. In the analyses that we performed we observed a significant decrease in prevalence of S. aureus in vaccinated cows compared to control cows, particularly later in lactation. Rate of new infection and prevalence of CNS tended to be lower in vaccinated cows compared to control cows. Duration of infection was significantly shorter in vaccinated cows compared to control cows in both S. aureus and CNS.