The invention especially relates to multivalent vaccine compositions that can treat or prevent at least 60, preferably 75% of infections caused by Neisseria meningitidis especially of serogroup B. To this end, the invention in particular provides a lipooligosaccharide (LOS) of N. meningitidis in particular constituted by a lipid A, an inner core, an α chain of L6 or L8 type, in which the heptose II residue of the inner core bears in position O-3 and in position O-6 or O-7 a phosphoethanolamine (PEA) substituent, and also to the construction of the strain of N. meningitidis that is capable of expressing such an LOS. The invention also relates to a strain of N. meningitidis of serogroup A that bears a lipooligosaccharide (LOS) in particular constituted by a lipid A, an inner core, an α chain of L6 type, in which the heptose II residue of the inner core bears in position O-3 a phosphoethanolamine (PEA) substituent and does not bear a PEA substituent in positions O-6 and O-7. The LOSs cited or originating from the mentioned strains may be used as vaccine antigens, especially in multivalent, e.g. divalent compositions, so as to offer protection against the major epidemiological complexes of N. meningitidis, especially of serogroup B.