Validation of a routine opsonophagocytosis assay to predict invasive pneumococcal disease efficacy of conjugate vaccine in children

Immunological evaluation of the clinical impact of vaccines designed to protect against infection by Streptococcus pneumoniae requires measurement of serotype-specific functional antibodies. We describe the development and validation of a viable pneumococcal opsonophagocytosis assay (OPA) that can be used for routine serological analysis of paediatric immune responses after immunization. OPA seropositivity (% ≥ 8 threshold) reflected well invasive pneumococcal disease (IPD) effectiveness. In contrast, the 22F inhibition ELISA seropositivity (% ≥ 0.20 μg/ml threshold) overestimated (19F) or underestimated (6B, 23F, 6A) IPD effectiveness for several serotypes. The seropositivity as estimated by a standardized and highly reproducible OPA was predictive for the serotype-specific IPD efficacy of pneumococcal conjugate vaccines.