Immune Memory of DTPw-HBV/Hib Vaccine Following Primary Vaccination, Immuno & Reacto of a Booster Dose Given in Infants

Inclusion criteria: For subjects receiving Plain PRP followed by DTPw-HBV: Male or female infant, 10 to 11 months of age, who previously completed the three-dose primary vaccination course with the DTPw-HBV/Hib vaccine. For subjects receiving DTPw-HBV/Hib or DTPw-HBV + Hib: Male or female infant, 15-18 months of age, who previously completed the three-dose primary vaccination course with the DTPw-HBV/Hib vaccine. For all subjects: * Subjects who the investigator believes that their parent/guardian can and will comply with the requirements of the protocol. * Free of obvious health problems as established by medical history and clinical examination Exclusion criteria: * Use of any investigational or non-registered product other than the study vaccine(s) within 30 days preceding administration of the study vaccine, or planned use during the study period. * Chronic administration of immunosuppressants or other immune-modifying drugs within six months prior to administration of the study vaccine. * Planned administration/administration of a vaccine not foreseen by the study protocol starting 30 days before and ending 30 days after administration of the study vaccine with the exception of oral polio vaccine.