The present study intends to investigate the use as a booster of a dose of sanofi pasteur's Pneumo 23 vaccine in the second year of life following 3-dose priming with Wyeth's Prevnar vaccine. The researchers will use a cohort of subjects who have received 3 doses of Prevnar® at 2, 4, 6 months of age in the context of the clinical study A3L12 on Hexavalent combined vaccine (DTaP-IPV-HB-PRP~T)

Inclusion Criteria:

• Aged 12 to 18 months on the day of inclusion
• Informed consent form signed by the parent/legally acceptable representative and by an independent witness if requested by local Ethics Committee regulation or/and if the parent/legally acceptable representative is illiterate
• Child having completed the three-dose primary vaccination of Prevnar® in the hexavalent combined vaccine study (study A3L12).
• Subjects and parent/guardian able to attend all scheduled visits and comply with all study procedures

Exclusion Criteria:

• Participation in another clinical study investigating a vaccine, drug, medical device, or a medical procedure in the 4 weeks preceding the study vaccination
• Planned participation in another clinical study during the present study period
• Known or suspected congenital or acquired immunodeficiency, immunosuppressive therapy such as long-term systemic corticosteroids therapy
• Known systemic hypersensitivity to any of the vaccine components or history of a life-threatening reaction to the study vaccine or to a vaccine containing any of the same substances
• Chronic illness at a stage that could interfere with study conduct or completion, in the opinion of the investigator
• Receipt of blood or blood-derived products since birth that might interfere with the assessment of immune response
• Receipt of any vaccine in the 4 weeks preceding the study vaccination
• Planned receipt of any vaccine in the 4 weeks preceding or following study vaccination
• History of seizures Known personal Human Immunodeficiency Virus (HIV), Hepatitis B (HB) antigen or Hepatitis C seropositivity
• History of pneumococcal infection (confirmed either clinically, serologically or microbiologically)
• Previous booster vaccination against the pneumococcal disease with either the study vaccine(s) or another vaccine
• Thrombocytopenia, bleeding disorder or anticoagulants in the 3 weeks preceding inclusion contraindicating IM vaccination
• Febrile illness (temperature ≥ 38°C) or moderate or severe acute illness/infection on the day of vaccination, according to investigator judgment.