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

AIMS To describe the age-specific seroprevalence of group B serum bactericidal antibody (SBA) and anti-outer membrane vesicle (OMV) IgG antibody, in order to establish a baseline seroprevalence in England and inform our understanding of the correlates of protection for group B disease. METHODS 2702 representative sera from the HPA Seroepidemiology Unit collected between 2000 and 2004 were selected and tested using a standardised complement-mediated SBA assay against strain NZ98/254, phenotype B:4:P1.7-2,4 (ST-42, complex ST-41/44). Specific IgG OMV ELISA end-point titres against OMV antigen preparations from target strain NZ98/254 were also determined. The results were compared with available data on meningococcal carriage, meningococcal disease and seroprevalence to group C meningococci in the pre-vaccination era. Simple mathematical models were also constructed. RESULTS 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 titres ≥4. During teenage years, there is a marked increase in the percentage of subjects with SBA titres ≥4, rising to over 50% in 19 year olds, with around 20% of older adults achieving this titre. Anti-OMV IgG GMTs remain fairly low and constant in 1-12 year olds, then GMTs increase with age, peaking at age 19 years and plateauing in adults. The peak in antibody titres coincides with the peak in meningococcal carriage. Simple mathematical models confirm that the relationship between observed seroprevalence and carriage by age is consistent, and that following an episode of carriage, SBA levels may remain elevated for a period of 1-4 years. Disease incidence is highest in children aged 3-11 months, when only around 4% have SBA titres ≥4, but disease incidence is low in children aged 2-11 years, even though putatively protective titres are observed in fewer than 7% of children. CONCLUSIONS The age-specific group B SBA profile is consistent with observed patterns of meningococcal carriage. The inverse relationship between disease incidence and SBA titres previously described was not found in this study, where SBA remained relatively low and stable as disease risk declined in 1-12 year olds.