Introduction Streptococcus pyogenes (Group A Streptococcus, Strep A) is a Gram-positive bacterium and one of the most significant global bacterial pathogens, with disproportionate disease burden affecting low and middle-income countries. Despite substantial mortality and immune sequelae caused by Strep A, no licensed vaccines exist, and correlates of protection remain unestablished. Advancing Strep A vaccine development requires standardized and qualified assays to accurately measure vaccine-induced immune responses to support vaccine development and licensure/post-licensure monitoring. This study reports a direct comparison of two qualified multiplex immunoassays designed to detect human IgG antibodies targeting four distinct Strep A vaccine antigens. Methods The MSD assay platform employs positional multiplexing with electrochemiluminescent detection, while the Luminex system uses bead-based multiplexing with fluorescent detection. Both assays used standardized intravenous immunoglobulin dilutions as reference standards. Assay precision was evaluated by analyzing eight samples from human volunteers selected to span the dynamic range for the four antigens Streptolysin O, S. pyogenes cell envelope protein, S. pyogenes adhesion and division protein, and group A carbohydrate. Results Both platforms demonstrated comparable intermediate precision and repeatability profiles. Increased variance was observed in samples with very low antibody concentrations. Neither operator variability nor day-to-day factors significantly impacted assay results. Additionally, inter-assay coefficients of variation for standards remained below 15% within the pre-established quantitative ranges for both platforms. Discussion The findings demonstrate that both multiplex immunoassays show equivalent precision and repeatability for quantifying human IgG to four Strep A vaccine antigens, making both platforms suitable for supporting early clinical trials and seroepidemiological studies.
Morici et al. (Thu,) studied this question.