In a multicentre field study , the incidence of new cases of Streptococcus uberis clinical intramammary infection in the group vaccinated with UBAC was 50% lower than the incidence in the placebo group (6.1% vs 12.2%) which was statistically significant different (p=0.012). Bearing in mind that some cows had suffered more than one episode of Streptococcus uberis clinical intramammary infection, the incidence of cows with clinical intramammary infection was 52.5% lower in the vaccinated group than those of the placebo group (4.7% versus 9.9%), with a statistical significance of p<0.017.