Pre-adsorption of sera with cps2 led to increased survival of cps14 (A) and decreased cps14-induced oxidative burst (B). Sera collected from animals 11 days post booster immunization, which showed an V3117/2‐induced oxidative burst > 5% (n = 7), were pre-adsorbed with the cps2 strain isolated from a diseased piglet not included in the challenge study. Pre-adsorbed and untreated control sera (ctr) were used to reconstitute porcine blood, which was either incubated with 3 × 105 CFU/mL of V3117/2 for bactericidal assay (A) or 6 × 106 CFU/mL of Cell Trace® FarRed-labbeld V3117/2 before adding dihydrorhodamine 123. Frequency of granulocytes showing both, oxidative burst and phagocytosis activity induced by cps14 strain V3117/2 was measured by flow cytometry (BD FACSCalibur and FlowJo) (B). Levels of IgG (C) and IgM (D) antibodies binding to the surface of cps14 were measured in non-adsorbed (ctr) and pre-adsorbed sera (cps2-pre ads.). Mean values are indicated by horizontal lines, standard deviations by error bars. Significant differences between treated and control sera were either determined using Wilcoxon matched pair test (A + C) or paired t-test (B + D) (*p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001).