Long-Term Persistence of Antibody following Immunization with Pneumococcal Polysaccharide Vaccine

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Abstract
Thirty-seven healthy volunteers who received a pneumococcal polysaccharide vaccine were tested 4, 5 or 6 yr after immunization for circulating type-specific pneumococcal antibody by radioimmunoassay of their sera. Each volunteer was immunized with 1 of 4 pneumococcal vaccines containing 50 .mu.g of each of 6, 8, 9 or 13 capsular polysaccharides; a few volunteers received octavalent or tridecavalent pneumococcal vaccines combined with bivalent influenza virus vaccine in a single syringe. Four years after immunization, the mean antibody level was 90% of the level achieved 4 wk after vaccination. Among volunteers tested 5 yr after immunization (including 3 volunteers 6 yr after vaccination), the mean antibody level was 76% of that 4 wk after inoculation. These findings confirm the long-term persistence of vaccine-induced type-specific pneumococcal antibodies and suggest that the interval between repeated doses of pneumococcal vaccine should be at least 5 yr.