Seroprevalence of bactericidal and anti-outer membrane vesicle antibody to Neisseria meningitidis group B in England

Outer membrane vesicle (OMV) and recombinant protein based vaccines targeted against multiple strains of group B meningococci are under development. The serum bactericidal antibody (SBA) assay has been designated the surrogate of protection, but the exact cut-off has not been determined. We measured SBA titers in 2,415 and anti-OMV IgG antibody concentrations in 2,672 sera representative of the UK population to establish a baseline of natural immunity. SBA and anti-OMV IgG antibodies are high in infants in the first 3 months of life, declining thereafter, presumably as maternal immunity wanes. Around 6% of subjects in the 1 to 11 year old age group had SBA titers ≥4. During teenage years, there is a marked increase in the percentage of subjects with SBA titers ≥4, rising to over 50% in 19 year olds, with around 20% of older adults achieving this titer. The peak in SBA and anti-OMV IgG titers coincides with the peak in meningococcal carriage. Simple mathematical models confirm that the relationship between observed seroprevalence and carriage by age is consistent with carriage inducing SBA, and that following an episode of carriage, SBA levels may remain elevated for many months. With the exception of children aged 3-11 months, there was no clear relationship between disease incidence and seroprevalence.