Population-based seroprevalence of Neisseria meningitidis serogroup C capsular antibody before the introduction of conjugate vaccine, in Australia

Neisseria meningitidis serogroup C (NMC) conjugate vaccine was introduced, in Australia, in 2003. Our aims were to determine pre-immunisation IgG NMC seroprevalence and evaluate an enzyme-linked immunosorbent assay (ELISA), previously validated against the serum bactericidal assay (SBA). 2409 sera, collected in 2002, from subjects aged 2–34 years, were tested. The geometric mean concentration (GMC) of NMC anticapsular IgG was 0.38 U/mL in subjects under 19 years and it increased to 0.67 U/mL for those aged 30–34 years. Variation in GMC correlated with reported NMC disease incidence and was higher in males than females (0.52 U/mL versus 0.41 U/mL; p = 0.005). The ELISA appears suitable for serosurveillance but the IgG level that correlates with protection needs further investigation. Serosurveys will be repeated to monitor the impact of vaccination.