Reduced-antigen, combined diphtheria, tetanus, and three-component acellular pertussis vaccine (Tdap; Boostrix(®)) is indicated for booster vaccination against diphtheria, tetanus, and pertussis. In clinical trials, a single booster dose of Tdap induced high seroprotective levels of antibodies to its three component acellular pertussis antigens in virtually all children and adolescents, and in a high proportion of adults and elderly individuals, at ≈1 month post-vaccination, irrespective of their vaccination history. Seropositivity rates for antibodies against pertussis toxin had begun to decline by 5 years after a booster dose of Tdap in adolescents/adults, with a subsequent booster dose 10 years later generally as immunogenic and as well tolerated as the initial booster. Tdap was safe and well tolerated in all age groups.