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Context Increasing reports of pertussis among US adolescents, adults, and their infant contacts have stimulated vaccine development for older age groups.Objective To assess the immunogenicity and reactogenicity of a tetanus-diphtheria 5-component (pertussis toxoid, filamentous hemagglutinin, pertactin, and fimbriae types 2 and 3) acellular pertussis vaccine (Tdap) in adolescents and adults.Design, Setting, and Participants A prospective, randomized, modified doubleblind, comparative trial was conducted in healthy adolescents and adults aged 11 through 64 years from August 2001 to August 2002 at 39 US clinical centers.Interventions A single 0.5-mL intramuscular dose of either Tdap or tetanusdiphtheria vaccine (Td).Main Outcome Measures Antibody titers to diphtheria and tetanus toxoids for Tdap and Td were measured in sera collected from subsets of adolescents and adults, before and 28 days after vaccination. For pertussis antigens, titers in sera from Tdap vaccinees were assessed vs those from infants who received analogous pediatric diphtheria-tetanus-acellular pertussis vaccine (DTaP) in a previous efficacy trial. Safety was assessed via solicited local and systemic reactions for 14 days and adverse events for 6 months following vaccination.Results A total of 4480 participants were enrolled. For both Tdap and Td, more than 94% and nearly 100% of vaccinees had protective antibody concentrations of at least 0.1 IU/mL for diphtheria and tetanus, respectively. Geometric mean antibody titers to pertussis toxoid, filamentous hemagglutinin, pertactin, and fimbriae types 2 and 3 exceeded (by 2.1 to 5.4 times) levels in infants following immunization at 2, 4, and 6 months with DTaP. The incidence of solicited local and systemic reactions and adverse events was generally similar between the Tdap and Td groups.Conclusions This Tdap vaccine elicited robust immune responses in adolescents and adults to pertussis, tetanus, and diphtheria antigens, while exhibiting an overall safety profile similar to that of a licensed Td vaccine. These data support the potential routine use of this Tdap vaccine in adolescents and adults.

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