Study Evaluating 13-valent Pneumococcal Conjugate Vaccine (13vPnC) in Children With Sickle Cell Disease

This study is to evaluate the safety, tolerability and immunogenicity of 13-valent pneumococcal Conjugate Vaccine in children with Sickle Cell Disease who have already been vaccinated with 23-valent polysaccharide vaccine. The study will measure the amount of antibodies (the proteins that fight off germs) produced by children with Sickle Cell Disease after they have been given the 13-valent pneumococcal vaccine between 6 and less than 18 years of age. They will be given the vaccination twice, each vaccination separated by approximately 6 months.