Meningococcal serogroup C-specific IgG antibody responses and serum bactericidal titres in children following vaccination with a meningococcal A/C polysaccharide vaccine.

In the UK, a co-ordinated series of phase II studies is being undertaken with meningococcal serogroup C conjugate (MCC) vaccines. The use of meningococcal A/C polysaccharide (MACP) vaccines in control arms in young children has been avoided because of the well recognised short comings of these vaccines. Following a cluster of serogroup C disease centred on a day nursery, intervention by MACP vaccination was performed as an outbreak control measure. Using this cohort, serogroup C-specific IgG ELISA and serum bactericidal assays (SBA) were performed using both de-O-acetylated (Oac(-)) and acetylated (Oac(+)) serogroup C antigen, the measurement of primarily high avidity antibody and using baby rabbit or human complement in the SBA. The effect of subject age (either less than or greater than 2 years of age) was assessed for the different assays and significant differences (P<0.05) were found using both antigen sources in the high avidity ELISA and in the rabbit complement SBA but not in the standard ELISA. When assessing results from different studies it is important that methodologies utilised allow such comparisons since the choice of reagents can have a profound influence. The importance of standardised assays is paramount at a time where immunogenicity trials are replacing efficacy trials for the introduction of MCC vaccines.