The aims of this study are to compare the immunogenicity and safety of the GSK Biologicals' combined DTaP-IPV vaccine with separate administration of DTaP and IPV vaccines, when administered as a fifth dose of acellular pertussis vaccine to children aged 4 to 6 years when co-administered with MMR vaccine in subjects who had previously received four doses of Infanrix, three doses of poliovirus-containing vaccine and MMR vaccination.

Open, randomized, phase II, clinical trial to compare the immunogenicity and safety of a booster dose of GSK Biologicals' DTaP-IPV vaccine (Infanrix®-IPV) co-administered with a booster dose of Merck and Company's M-M-R®II, to that of separate injections of GSK Biologicals' DTaP vaccine (Infanrix®), Aventis Pasteur's IPV (IPOL®) and M-M-R®II administered as booster doses to healthy children 4 to 6 years of age.

"Inclusion criteria Healthy children between and including 4 and 6 years of age. Previously received 4 doses of GSK Biologicals' DTaP, 3 doses of IPV vaccine and 1 dose of measles, mumps, and rubella vaccine.

Exclusion criteria Use of any investigational or non-registered drug or vaccine other than the study vaccines within 30 days preceding the administration of study vaccines, or planned use during the study period.

Chronic administration or planned administration of immunosuppressants or other immune modifying drugs within six months prior to study vaccination or planned administration during the study period Administration of immunoglobulins and/or blood products within 3 months prior to vaccination."