Disease susceptibility to ST11 complex meningococci bearing serogroup C or W135 polysaccharide capsules, North America.

Clusters of meningococcal disease caused by a hyperinvasive lineage of Neisseria meningitidis, the ST11 complex, bearing a serogroup C polysaccharide capsule, have been prominent in Europe and North America since the early 1990s. This situation has led to expensive public health measures for outbreak control and, finally, to the introduction of a serogroup C glyconjugate vaccine into the primary immunization schedule in the United Kingdom and elsewhere. ST11 complex meningococci may also express serogroup W135 polysaccharide capsules. We investigated the level of population immunity to this hyperinvasive clone in association with the appearance of outbreaks of meningococcal disease in southern British Columbia. We found that most adults and almost all children were apparently susceptible to infection with ST11 complex meningococci bearing both C and W135 polysaccharide capsules, which suggests that a vaccine program directed against only serogroup C meningococci may be insufficient to prevent hyperinvasive ST11 disease.