 Neisseria meningitidis causes meningitis and severe infections of the blood stream. The incidence of serogroup B meningococcal disease however is too low to conduct a randomized, controlled trial to determine the actual efficacy of the new serogroup B vaccines. Instead vaccine efficacy was inferred from serum bactericidal antibody responses using four test strains. However, because of strain variability of FHbp amino acid sequence there are more than 800 sequence variants described and strain variability of FHbp expression, bactericidal data on only four strains are unlikely to be sufficient to predict the actual strain coverage by the vaccine. There also are gaps in knowledge about the underlying mechanisms by which human antibodies to FHbp elicit complement mediated bactericidal activity. For example, binding of FH to FHbp is specific for human FH. Therefore in vaccinated humans the vaccine antigen is expected to form a complex with FH right after immunization. The investigators hypothesis is that binding of human FH to the vaccine antigen skews the antibody repertoire to FHbp epitopes located outside of the FH combining site. The resulting antibodies would be expected not to inhibit binding of FH to the bacteria. This hypothesis will be investigated in Trumenba-immunized humans as part of studies in Aim 1 and in future studies of recombinant human anti-FHbp Fabs that will be enabled by obtaining DNA from individual B cells, described in Aim 2. 