Infant immunization with pneumococcal CRM₁₉₇ vaccines: Effect of saccharide size on immunogenicity and interactions with simultaneously administered vaccines

Six pentavalent pneumococcal conjugate vaccines (Pn-CRM₁₉₇) were evaluated among 400 infants. The vaccines differed in saccharide chain length (oligosaccharide [OS] or polysaccharide [PS]) and saccharide quantity (0.5, 2, or 5 μg). Subjects were randomized into groups 1-6 (Pn-CRM₁₉₇ recipients) or 7 (controls) for immunization at 2, 4, and 6 months of age. Pn-CRM₁₉₇ were well tolerated and elicited mean antibody concentrations that exceeded those in controls for all 5 capsular serotypes. PS formulations were generally more immunogenic than their OS counterparts. For PS vaccines, a dose-response was documented (5 μg > 2 μg > 0.5 μg), but the differences between the 5- and 2-μg formulations were insignificant. The mean anti-PRP antibody concentration was significantly higher among Pn-CRM₁₉₇ recipients. It is concluded that PS vaccines are more immunogenic than OS vaccines. The improved immunogenicity from Haemophilus type b oligosaccharide conjugate (HbOC) vaccine when given with Pn-CRM₁₉₇ suggests that a decreased dose of HbOC vaccine may be sufficient to elicit protection.