Oxidative burst of granulocytes is not associated with immunization (A), but with reduced bacterial survival (B). S. suis strain V3117/2 (cps14)‐induced oxidative burst rates of granulocytes from blood samples drawn 11 d post booster did not reveal an immunization effect of the multicomponent vaccine, but showed correlation with the respective bacterial survival factors (SF). To determine oxidative burst induced by S. suis in granulocytes, 6 × 106 CFU/mL V3117/2 or PBS (negative-control) were added to the whole blood samples (11 dp booster) and incubated for 15 min at 37 °C in water bath and for further 10 min after addition of dihydrorhodamin 123 (5 μg/mL). Following erythrocyte lysis the samples were directly measured by flow cytometry. S. suis-induced oxidative burst rates were calculated as described in “Materials and methods”. A Comparison of S. suis-induced oxidative burst rates of placebo-treated (black circle) and vaccinated (grey square) animals. Statistical analysis was conducted with the unpaired t-test (two-tailed). B Spearman correlation between S. suis induced-oxidative burst rates with the respective bacterial survival factors of S. suis V3117/2 (cps14) in blood of all animals (n = 16) as shown in Figure 4. Animals that had to be euthanized after challenge with S. suis V3117/2 (cps14) due to a high clinical score are marked with white symbols (†n = 5).