Tolerability and immunogenicity of an eleven-valent pneumococcal conjugate vaccine healthy toddlers

Background. A need to increase the serotype coverage of pneumococcal conjugate vaccines exists. The use of a single carrier protein may cause overload of the carrier and decrease the immune response by not providing sufficient carrier-specific T helper cell support. A vaccine composed of a mixture of tetanus- and diphtheria-conjugated polysaccharides (PS) is a potential solution to this issue. Objectives. The aim of this study was to assess the tolerability and immunogenicity in healthy toddlers of an 11-valent pneumococcal conjugate vaccine that uses both tetanus and diphtheria toxoids as carriers. We explored the effect of an aluminum adjuvant on safety and immunogenicity by comparing the vaccine with and without adjuvant. Methods. Twenty Finnish and 23 Israeli toddlers received the conjugate vaccine with or without aluminum adjuvant. Safety data were recorded for 5 days after vaccination. Sera were obtained before and 28 days after the immunization. IgG antibodies to the 11 vaccine-type PSs were determined by enzyme immunoassay. Results. No serious adverse events occurred. The formulation with the adjuvant tended to induce fewer local but more systemic reactions than the non-adjuvant-containing formulation. Both vaccine formulations induced significant IgG increases for the vaccine-specific PSs. Types 3 and 7F were the most immunogenic; antibodies reached a concentration of 1 mug/ml in all individuals. Conjugates of types 6B, 14 and 23F were the weakest immunogens; antibodies reached the concentration of 1 mug/ml in 36, 27 and 32% of the individuals in the nonadjuvant group and in 53, 38 and 53% in the adjuvant group, respectively. Conclusions. An 11-valent mixed carrier pneumococcal conjugate vaccine is safe and immunogenic in toddlers. The use of an adjuvant do not seem to offer any significant benefit.