BACKGROUND: Immunogenicity and safety of stand-alone diphtheria, tetanus toxoid, 5-component acellular pertussis vaccine adsorbed, inactivated poliovirus (IPV) combination vaccine (DTaP5-IPV) was compared with separate DTaP5 plus IPV vaccines as fifth dose in children 4-6 years of age. METHODS: In this phase III, controlled, multicenter, randomized, open-label study, participants were randomized to DTaP5-IPV plus measles/mumps/rubella (MMR) and varicella virus (VZV) vaccines (group 1; N = 324), DTaP5+IPV with MMR and VZV (group 2; N = 327), DTaP5-IPV with/without MMR/VZV (group 3; N = 2419) or DTaP5+IPV with/without MMR/VZV (group 4; N = 302). Immunogenicity endpoints (groups 1 and 2) included booster response rates and antibody geometric mean concentrations (GMCs). Noninferiority of DTaP5-IPV to DTaP5+IPV was evaluated based on differences (groups 1 and 2) in booster rates and postvaccination GMC ratios. Safety endpoints (all groups) included all adverse events. RESULTS: Noninferiority of DTaP5-IPV compared with DTaP5+IPV for all antigens was achieved. Booster rate differences were 5.4% for pertussis toxoid (PT); 7.4% for filamentous hemagglutinin; 3.7% for pertactin (PRN); 4.8% for fimbriae types 2 and 3; -0.1% for tetanus; -1.9% for diphtheria; 3.7% for poliovirus 1; -0.7% for poliovirus 2 and 0.3% for poliovirus 3. GMC ratios were 1.97 for PT; 1.56 for filamentous hemagglutinin; 1.51 for PRN; 1.33 for fimbriae types 2 and 3; 1.17 for tetanus; 1.20 for diphtheria; 1.27 for poliovirus 1; 0.90 for poliovirus 2 and 1.34 for poliovirus 3. Rates of immediate and unsolicited adverse events, solicited injection site reactions and systemic reactions were similar between groups. CONCLUSIONS: DTaP5-IPV was safe and immunogenic in children 4-6 years of age.