Simultaneous evaluation of molecular size and antigenic stability of PNEUMOVAX 23, a multivalent pneumococcal polysaccharide vaccine.

A technique using high performance size exclusion chromatography (HPSEC) with rate nephelometry (RN) detection has been developed to simultaneously measure the relative molecular size and antigenicity of the bacterial polysaccharide components in a multivalent pneumococcal vaccine, PNEUMOVAX 23. This assay was used to establish stability profiles for each of the 23 pneumococcal polysaccharide serotypes in this vaccine formulation, based on concurrent analyses of vaccine lots up to nine years of age. The exceptional inter-assay precision (<1% RSD) permitted detailed analysis of the data and a more accurate measure of the stability of this product that heretofore has not been available. While 21 of the 23 serotypes in the vaccine show essentially no change in molecular size over several years, serotypes 19A and 19F show changes in relative molecular size of approximately 2% per year. Similar decreases in relative molecular size for serotypes 19A and 19F stored in aqueous formulation have also been observed in other commercially available pneumococcal vaccine products. Additionally, stability profiles of relative antigenicity for nine of the 23 serotypes are reported based on information that is simultaneously obtained in the HPSEC/RN analysis. Of the nine serotypes examined, only serotypes 1, 9V and 18C demonstrate antigenic lability over time, in each case showing a decrease in antigenicity on the order of 5% to 10% per year. Overall, this method is a precise and efficient means of providing data on relative molecular size and relative antigenicity for each polysaccharide component of a multivalent vaccine product. Application of this method in stability studies of such vaccines provides critical information for evaluating time-dependent changes in these products.