Individual polysaccharide quantification in polyvalent pneumococcal conjugate vaccine using rate nephelometry

The multivalent pneumococcal conjugate vaccine (PCV) contains purified polysaccharides of different serotypes conjugated to a carrier protein. Testing the final formulated product for individual serotype polysaccharide content is critical in vaccine quality control which requires an assay specific to each serotype polysaccharide present in the formulated product. Antibodies specific to the serotypes specific polysaccharide were used in rate nephelometry assay for quantifying individual serotype polysaccharides in the formulated vaccine. Generally, native polysaccharide (NP) have been used as reference standard. However, the polysaccharide antigen in the vaccine product is in the conjugate form (CRM₁₉₇ linked) and hence using NP as a reference standard may not be suitable. Activated quenched polysaccharide (AQP) as a reference standard in rate nephelometry would be more appropriate. The epitope structure of AQP closely represents the polysaccharide-protein conjugate drug product (DP) after trypsin digestion. Hence, AQP was evaluated as a novel reference standard for the accurate and precise determination of individual polysaccharides in the multivalent DP. Rate nephelometry assay using AQP could be used for DP release and stability for monitoring time-dependent changes in the product and establishing the shelf life. A similar strategy could be applied to test and release monovalent or multivalent polysaccharide-protein conjugate vaccines (Meningococcal, Haemophilus influenza Type B, Typhoidal, and non-typhoidal salmonella).