Immune response to octavalent diphtheria- and tetanus-conjugated pneumococcal vaccines is serotype- and carrier-specific: The choice for a mixed carrier vaccine

Background. Development of protein-conjugated pneumococcal vaccines for infants has led to formulations that are immunogenic in the age group at highest risk for pneumococcal diseases. This study focuses on the search for an optimal formulation. Methods. In a randomized trial Icelandic infants (n = 160) were immunized at age 3, 4 and 6 months with one of two octavalent pneumococcal conjugate vaccines (serotypes 3, 4, 6B, 9V, 14, 18C, 19F and 23F conjugated to diphtheria toxoid (PncD) or tetanus protein (PncT) followed with a booster of either the same conjugate or 23-valent polysaccharide vaccine at 13 months. Safety data were collected after each vaccination, and IgG responses (enzyme-linked immunosorbent assay) were measured at 3, 4, 6, 7, 13 and 14 months. Results. Both conjugates were safe and caused fewer local reactions than the routine vaccines (P < 0.0001). At 7 months both groups had significant IgG response to all serotypes. The geometric mean concentration range was 0.35 to 4.09 and 0.65 to 3.38 μg/ml for PncD and PncT, respectively, with 88.2 to 100% and 92.4 to 100% of subjects reaching ≥0.15 μg/ml. The PncD gave better primary responses to serotypes 3, 9V and 18C, whereas PncT gave better response to serotype 4. Similar responses were induced to the other serotypes. Good booster IgG responses were obtained in all vaccine groups; 97.5 to 100% of subjects reached ≥1 μg/ml. Conclusions. Both octavalent pneumococcal conjugates were safe and immunogenic in infants. Based on the results from this and similar trials, a mixed diphtheria and tetanus pneumococcal conjugate vaccine was designed to provide the optimal immune response to each serotype.