To optimize the safety and immunogenicity of pneumococcal conjugate vaccines (PCV), the following issues related to vaccine formulation need to be considered: the quantity of each serotype-specific polysaccharide (PS), total quantity of PS, total quantity of protein carrier, ratio of PS to carrier, and the carrier protein of concurrently administered Hib conjugate vaccines. We performed a study to evaluate some of these factors with two lots of a heptavalent PCV (serotypes 4, 6B, 9V, 14, 18C, 19F, and 23F) employing the outer membrane protein complex (OMPC) of N. meningitidis serogroup B as the carrier. Compared to lot 1, lot 2 contained higher quantities of serotypes 6B, 18C, and 23F PS, and had more total PS and OMPC. At 2, 4, and 6 months of age, 40 infants were given PCV lot 1 concurrent with PRP-OMP (7.5μg dose at 2, 4 mo) and PRP-T (6 mo) (Grp A), 60 infants were given PCV lot 2 concurrent with HbOC (Grp B), and 60 infants were given PCV lot 2 concurrent with PRP-OMP (3 μg dose) (Grp C). No serious PCV-attributable adverse reactions were reported. In this study, a higher dose of PS conjugate did not enhance serotype-specific immune responses (see table). Concurrent use of PRP-OMP vaccine did not diminish the immune response of PCV, except for serotype 6B (Grp C). Both lots of PCV were immunogenic and are promising candidates for a vaccine efficacy trial to prevent invasive pneumococcal disease in infants. Supported by Merck & Co., Inc.

Table 1