The purpose of this study was to evaluate the immunogenicity of the booster immunization with pneumococcal conjugate vaccine in Korean children.

Thirty-nine children aged 12-23 months who visited Kangnam CHA Hospital between September 2006 and December 2006 were enrolled. The children were divided into primary and booster groups depending on their vaccination status for the 7-valent pneumococcal conjugate vaccine. The anti-pneumococcal antibody levels of each serotype included in the vaccine (4, 6B, 9V, 14, 18C, 19F, 23F) were determined by third-generation ELISA.

The geometric mean titer (GMT) of antibodies to each pneumococcal serotype in the booster group was higher than in the primary group ( P <.05). The percentage of subjects with pneumococcal antibodies ≥0.35 µg/mL was 90.5-100% for all serotypes in both the primary and booster groups. The percentage of subjects with pneumococcal antibodies ≥1.0 g/mL in the booster group was 94.4-100%, which was higher than the primary group except for serotypes 6B and 14 ( P <.05). The percentage of subjects with pneumococcal antibodies ≥5.0 µg/mL in the booster group was 50.0-94.4% which was higher than the primary group for all serotypes ( P <0.05).

The immunogenicity of a booster dose of the pneumococcal conjugate vaccine in Korean children was high and the immunogenicity of a primary series was also relatively high. To determine the feasibility of the introduction of the pneumococcal conjugate vaccine and the appropriate schedule for Korean children, further prospective investigation of the immunogenicity of the booster immunization is needed.