Prevention of pneumococcal bacteremia by immunization with type 6 pneumococcal capsular polysaccharide vaccine in splenectomized rats

Postsplenectomy sepsis is well recognized and prophylactic vaccination with pneumococcal polysaccharide is recommended. However, the efficacy of vaccination with the polysaccharide in splenectomized individuals is not clear. The effect of type 6 pneumococcal polysaccharide vaccine on the clearance of pneumococci from the bloodstream and lung was studied in splenectomized rats as was survival after intravenous challenge with Streptococcus pneumoniae, serum opsonic activity, and specific antibody titer by ELISA. Rats immunized with type 6 pneumococcal polysaccharide vaccine had significantly increased survival (P less than .05) and clearance of pneumococci from the bloodstream and lung (P less than .05) after intravenous challenge with S. pneumoniae, significantly higher serum opsonic activity (P less than .02), and increased specific IgG and IgM antibody titer to the type 6 polysaccharide compared with controls treated with saline. There was close correlation between IgG antibody titer to type 6 polysaccharide and opsonic activity (r = .95). These results suggest that pneumococcal polysaccharide vaccine is effective for preventing pneumococcal bacteremia in splenectomized hosts.