This study aims to evaluate the immunogenicity and reactogenicity of 13-valent pneumococcal conjugate vaccine among infants, toddlers and children in Bobo-Dioulasso, Burkina Faso. Infants will be randomized to receive vaccine at 6, 10, 14 weeks or at 6 weeks, 14 weeks and 9 months of age. Serotype-specific serum IgG, OPA and nasopharyngeal colonization will be assessed at 6 weeks, 18 weeks, 9 months and 10 months of age. Toddlers 12-15 months of age will be randomized to receive either a single dose of PCV13 or 2 doses 2 months apart. Serotype-specific serum IgG and OPA will be measured pre-dose 1 and again 3 months later. Children 2 to 4 years of age will receive a single dose of PCV13 and have IgG and OPA assessments pre-vaccination and 1 month post-vaccination.