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.

The immunogenicity and reactogenicity of PCV13 in the "standard schedule" groups (e.g. 6, 10, 14 weeks for infants and single dose for toddlers) will be compared to that observed in the PCV13 licensure trials. Within each age group the alternative schedule will be compared to the standard schedule in terms of immunogenicity and impact on nasopharyngeal carriage (infants only).

Infants inclusion criteria

• Child has birth weight ≥ 2500g
• Child was born at ≥ 37 weeks of pregnancy or judged to be full-term by midwife or birth attendant
• Mother has resided in Burkina Faso for at least 2 years
• Mother has African nationality
• Child will reside in Bobo-Dioulasso urban area for the duration of the study
• Parent or guardian has given informed consent for child's participation

Infants exclusion criteria

• Child was born with a congenital abnormality
• Child has chronic or acute severe illness requiring specialized medical care
• Child has a blood coagulation disorder
• Mother has known HIV infection
• Child is enrolled in another clinical trial
• Child has known allergy to a component of the vaccine
• Child received a pneumococcal vaccine outside the context of the trial
• Child is 53 days of age or older at 6 week visit
• Child weighs <3500g at the 6 week visit
• Blood draw at 6 week visit was unsuccessful after 3 attempts

Toddlers inclusion criteria

• Child is 12 to 15 months of age
• Child has resided in Burkina Faso since birth
• Child has African nationality
• Child will reside in Bobo-Dioulasso urban area for the duration of the study
• Parent or guardian has given informed consent for child's participation

Toddlers exclusion criteria

• Child has visible signs of severe malnutrition
• Child has chronic or acute severe illness requiring specialized medical care
• Child has a blood coagulation disorder
• Child has known HIV infection
• Child is enrolled in another clinical trial
• Child has known allergy to a component of the vaccine
• Child received a pneumococcal vaccine outside the context of the trial
• Child's weight at first vaccination visit is lower than the 5th percentile of Burkinabe children (8.0 to 8.7 kg according to age)
• Blood draw at first vaccination visit was unsuccessful after 3 attempts

Children inclusion criteria

• Child is 2 to 4 years of age
• Child has resided in Burkina Faso since birth
• Child has African nationality
• Child will reside in Bobo-Dioulasso urban area for the duration of the study
• Parent or guardian has given informed consent for child's participation

Children exclusion criteria

• Child has visible signs of severe malnutrition
• Child has chronic or acute severe illness requiring specialized medical care
• Child has a blood coagulation disorder
• Child has known HIV infection
• Child is enrolled in another clinical trial
• Child has known allergy to a component of the vaccine
• Child received a pneumococcal vaccine outside the context of the trial
• Child's weight at first vaccination visit is lower than the 5th percentile of Burkinabe children
• Blood draw at first vaccination visit was unsuccessful after 3 attempts