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Conjugation of carbohydrate antigens to protein carriers significantly improves the immune response to many carbohydrates. In order to evaluate the potential for this approach to improve the performance of pneumococcal vaccine in the elderly, we evaluated pneumococcal polysaccharide-derived oligosaccharides conjugated to cross-reacting material 197 (CRM197) (CRM-OS) in 49 older adults over 60 years of age (median age, 66 years) and compared the results to those from 50 younger adults under age 45 (median age, 27 years). Subjects were randomly assigned to receive licensed 23-valent polysaccharide vaccine (PS) which contain 25 micrograms of polysaccharide per serotype, or 5-valent CRM-OS, which contains 10 micrograms of oligosaccharide per serotype, in double-blind fashion. Both vaccines were associated with moderate local pain on administration. Antibody responses to type 14 were seen in the majority of both younger and older subjects following administration of both CRM-OS and PS, and there was no significant improvement of responses with CRM-OS in either age group. Antibody responses in young adults to the less immunogenic type 6B were seen in only 36% of subjects receiving PS and in 56% of subjects receiving CRM-OS (P = 0.15), and the geometric mean 6B titer 1 month after vaccination was higher in CRM-OS recipients (10.9 versus 3.7 micrograms/ml; P = 0.04). However, 6B responses were poor following the administration of either vaccine to elderly adults and there was no difference between results with CRM-OS and those with PS in this age group. Relatively few subjects developed measurable mucosal immunoglobulin A responses in nasal secretions following administration of either vaccine. Revaccination of CRM-OS recipients with PS at 2 months did not result in significant additional responses to 6B or 14. Though CRM-OS is possibly more immunogenic in young adults, the formulation of the pneumococcal glycoconjugate vaccine used in this study does not appear to offer an advantage to the elderly for types 6B or 14.