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Meningococcal meningitis is a severe, life-threatening infection for which no adequate vaccine exists. Current vaccines, based on the group-specific capsular polysaccharides, provide short-term protection in adults against serogroups A and C but are ineffective in infants and do not induce protection against group B strains, the predominant cause of infection in western countries, because the purified serogroup B polysaccharide fails to elicit human bactericidal antibodies. Because of the poor immunogenicity of group B capsular polysaccharide, different noncapsular antigens have been considered for inclusion in a vaccine against this serogroup: outer membrane proteins, lipooligosaccharides, iron-regulated proteins, Lip, pili, CtrA, and the immunoglobulin A proteases. Alternatively, attempts to increase the immunogenicity of the capsular polysaccharide have been made by using noncovalent complexes with outer membrane proteins, chemical modifications, and structural analogs. Here, we review the strategies employed for the development of a vaccine for Neisseria meningitidis serogroup B; the difficulties associated with the different approaches are discussed.

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We describe an atypical presentation of bacteremia caused by N. meningitidis serogroup X. By multilocus sequence typing the isolate was characterized to the sequence type 2139, which is not related with the clonal complex recently isolated in Africa. Since 1984, only six cases of serogroup X N. meningitidis infections have been diagnosed in Spain. Nevertheless, after the application of the conjugated vaccine, attention should be paid to the emergence of infections caused by unusual serogroups of N. meningitidis.

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