Abstract
Boosting immunity to tetanus, diphtheria, and pertussis through the use of Tdap vaccines is routinely recommended at 11 to 12 years of age; some states, however, require Tdap for entry into middle school, which may begin at 10 years of age. This study was conducted to determine whether Tdap5 (Adacel), which is licensed for use in children beginning at 11 years of age, is as safe and immunogenic in 10-year-olds as it is in 11-year-olds. Children who had received 5 previous doses of any diphtheria-tetanus-acellular pertussis (DTaP) vaccine were enrolled in a phase IV clinical trial; 646 10-year-olds and 645 11-year-olds completed the study, which involved a single intramuscular dose of Tdap5 along with pre- and postvaccination serologies. Postvaccination geometric mean concentrations (GMCs) of antibody to pertussis antigens (pertussis toxoid, filamentous hemagglutinin, pertactin, and fimbria types 2 and 3) of 10-year-olds were noninferior to those of 11-year-olds, as were booster response rates for all pertussis antibodies, except for those to fimbrial antigens (94% and 97%, respectively). Seroprotection rates among 10-year-olds for tetanus and diphtheria were noninferior to those in 11-year-olds. Rates of injection site reactions, solicited systemic reactions, and unsolicited adverse events, adverse reactions, and serious adverse events were similar in the two groups. These data support the conclusion that Tdap5 is safe and immunogenic in 10-year-olds. (This study has been registered at ClinicalTrials.gov under registration no. NCT01311557.).