Abstract: The invention is directed to an immunity providing B cell activating molecule derived from a meningococcal lipopolysaccharide (LPS) having at least one epitope, said molecule comprising at least the communal part of the oligosaccharide part (core region) of lipopolysaccharides specific for at least two meningococcal immunotypes, preferably immunotypes L2 and L3 and wherein in galactose is absent in the B cell activating part, as well as derivatives of the molecules with immuno reaction inducing capacity. The invention is also directed at an outer membrane vesicle provided with a group of polypeptides having at least the immunoactivity of outer membrane proteins (OMP's) bound to a membrane, a polypeptide from the group of said outer membrane vesicles being a membrane anchored OMP or OMP fragment with a mutation in one of the surface loops, preferably in a 2, 3, 5, 6, 7 or 8-loop of a class I OMP.