Immunogenicity of a Streptococcus pneumoniae type 4 polysaccharide--protein conjugate vaccine is decreased by admixture of high doses of free saccharide.

In this study we report that the priming capacity of a Streptococcus pneumoniae type 4 polysaccharide-protein conjugate to booster immunizations with the native capsular polysaccharide is dose dependent. Furthermore, it is shown by admixture experiments that simultaneous administration of high doses of free saccharide (0.5-25 micrograms) of different chain lengths (varying from M(r) 1.6-120 kDa) decreases the anti-polysaccharide antibody response. Presence of low doses of saccharide (up to 10%), which are usually present in conjugates prepared by the carbodiimide coupling procedure, did not influence the anti-polysaccharide antibody response in adult and neonatal mice.