Correlations between IRPA and functional (SBA [a] and OPA [b]) or quantitative antibody (c to f) assays for the prevaccination sera from Icelandic teenagers (n = 26). Strain 44/76-SL (B:15:P1.7,16) was used in IRPA, SBA, OPA, and preparation of the OMVs, and in measurement of IgG binding to live cells. (a) SBA titers versus protection indices (PIs); (b) OPA titers versus PIs; (c) anti-OMV IgG concentrations versus PIs; (d) IgG binding to live 44/76-SL cells versus PIs; (e) anti-B-PS IgG concentrations versus PIs; (f) anti-B-PS IgM concentrations versus PIs.