Total and serotype-specific pneumococcal antibody titres in children with normal and abnormal humoral immunity.

A heptavalent pneumococcal conjugate vaccine (PCV-7) protects children against invasive pneumococcal disease. The aim of this study was to evaluate immunoglobulin subclass and serotype-specific pneumococcal antibody responses to vaccination in children with a history of recurrent or severe bacterial infections. Pneumococcal IgG, IgG1, IgG2 titres were assayed by ELISA, and nine serotype concentrations measured using a nonaplex bead assay in 145 children investigated for recurrent or severe infections. Children mounted an exclusively IgG1 response after vaccination with two doses of PCV-7 and a dose of 23 valent pneumococcal polysaccharide vaccine (PPV-23), with pneumococcal IgG2 antibody titres remaining low to negligible. Measurement of serotype-specific responses demonstrated that although PCV-7 specific serotype responses increased significantly post-vaccination, specific IgG against two of the serotypes not covered by PCV-7 but only by PPV-23 remained low. We conclude that in contrast to antibody response to natural infection with Pneumococcus or pneumococcal polysaccharide vaccines which are often of a IgG2 subclass, responses in children after PCV-7 are of IgG1 subclass. Serotype-specific IgG were useful in determining the protection against specific pneumococcal strains, and showed that the PPV-23 did not broaden protection against non-PCV-7 serotypes.