Therefore, a newly developed phagocytosis assay based on flow cytometry (flow assay) was using sera obtained from rabbit postvaccination with a bivalent conjugate of Neisseria meningitidis serogroup A capsular polysaccharide (CPSA) to serogroup B outer membrane vesicle containing PorA (OMV-PorA), an OMV-PorA of Neisseria meningitidis serogroup B and the CPSA (as control), was done in order to evaluation of the potential efficacy of (experimental) meningococcal vaccines.