Safety and immunogenicity of tetravalent pneumococcal vaccines containing 6B, 14, 19F and 23F polysaccharides conjugated to either tetanus toxoid or diphtheria toxoid in young infants and their boosterability by native polysaccharide antigens

New vaccines against pneumococcal infections in infancy are needed. We assessed in young infants the safety and immunogenicity of two tetravalent vaccines containing pneumococcal 6B, 14, 19F and 23F polysaccharides conjugated to either tetanus toxoid (Pnc-T) or diphtheria toxoid (Pnc-D). Pnc-T or Pnc-D containing 3 microg of polysaccharide of each of the four pneumococcal polysaccharides or placebo were given intramuscularly in a double blinded fashion (25 infants per group) at 2, 4 and 6 months of age. At 12 months of age all 75 children were boosted with a 23-valent nonconjugate polysaccharide pneumococcal vaccine. Serum type-specific anticapsular antibody concentrations were measured at 2, 4, 6, 7, 12 and 13 months of age. Adverse events occurring within 72 h after each injection were recorded. Both Pnc-T and Pnc-D were well-tolerated. Pnc-T and Pnc-D had higher antibody concentrations compared with placebo after primary immunity (type 6B, 1.66, 1.40 and 0.60 microg/ml, respectively; type 14, 4.81, 2.65 and 2.22 microg/ml, respectively; type 19F, 2.40, 3.48 and 0.83 microg/ml, respectively; type 23F, 0.96, 0.44 and 0.35 microg/ml, respectively). Proportions of infants with concentrations above 1.0 microg/ml were also higher in the vaccine recipients than in those given placebo. After booster with the nonconjugate polysaccharide vaccine, both geometric antibody concentration and proportion with concentrations > or =1.0 microg/ml were significantly higher among either Pnc-T or Pnc-D recipients than among placebo recipients. Both Pnc-T and Pnc-D were well-tolerated, induced serotype-specific anticapsular antibodies and induced immunologic memory.