Immunogenicity, Safety and Reactogenicity Study of GSK Biologicals' Pneumococcal Vaccine (Synflorix™) When Administered to Children Who Are at an Increased Risk of Pneumococcal Infection

The purpose of this study is to evaluate the immunogenicity, safety and reactogenicity of GSK Biologicals' 10Pn-PD-DiT vaccine in children aged between 2 and 17 years of age having asplenia, splenic dysfunction or complement deficiencies. In addition, this study will include an age-matched control group of healthy children aged 24-59 months in order to descriptively compare the immunogenicity of 10Pn-PD-DiT vaccine in the at-risk population to that of the general, healthy population one month after each pneumococcal vaccination.