Scientific Publications by FDA Staff

Clin Vaccine Immunol 2009 Jul;16(7):969-77

Investigation of different group A immunoassays following either one dose of meningococcal group A conjugate vaccine or A/C polysaccharide vaccine in adults.

Findlow H, Plikaytis BD, Aase A, Bash M, Chadha H, Elie C, Laher G, Martinez J, Herstad T, Newton E, Viviani S, Papaspyridis C, Kulkarni P, Wilding M, Preziosi MP, Marchetti E, Hassan-King M, La Force FM, Carlone G, Borrow R

A double-blind, randomized, controlled phase I study to assess safety, immunogenicity and antibody persistence of a new group A conjugate vaccine (PsA-TT) in volunteers aged 18-35 years was previously performed. Subjects received one dose of either the PsA-TT conjugate vaccine, meningococcal A/C polysaccharide vaccine (PsA/C) or tetanus toxoid vaccine. The conjugate vaccine was shown to be safe and immunogenic as demonstrated by a standardized group A-specific IgG ELISA and by a serum bactericidal antibody (SBA) assay using rabbit complement (rSBA). This report details further analysis of the sera using four additional immunologic assays, to investigate the relationship between the different immunoassays. The immunoassays used were; an SBA assay that used human complement (hSBA), a group A-specific IgG multiplexed bead assay and two opsonophagocytic antibody (OPA) assays which used two different methodologies. For each vaccine group, geometric mean concentrations (GMC) or geometric mean titers (GMT) were determined for all assays pre-, 4, 24 and 48 weeks post-vaccination. Pearsons correlation coefficients were used to assess the relationship between the six assays using data from all available visits. An excellent correlation was observed between the group A-specific IgG concentrations obtained by ELISA and multiplexed bead assay. hSBA and rSBA titers correlated moderately, although proportions of subjects with putatively protective titers and those demonstrating a >/= 4-fold rise were similar. The two OPA methods correlated weakly and only achieved low correlation to the other immunoassays. The correlation between hSBA and group A-specific IgG was higher for the PsA-TT group than the PsA/C group.