Pertussis is a highly contagious, vaccine-preventable disease for which a whole-cell vaccine (killed bacteria), in combination with toxoids against diphtheria and tetanus (DTwP), was introduced for immunization of children in the United States in the 1940s. With the eventual widespread use of DTwP vaccine, the national annual incidence of reported cases of pertussis decreased at least 150- to 200-fold, with only 1010 reported cases in 1976.1 Because of high rates of both local and systemic adverse events associated with DTwP vaccine, acellular pertussis vaccines (DTaP) that contain a small number of purified antigens of Bordetella pertussis and have far fewer adverse effects replaced DTwP vaccine in the 1990s. The DTaP vaccine is currently recommended for both primary (3 doses administered at 2, 4, and 6 months of age) and booster (2 doses administered at 15 to 18 months and 4 to 6 years of age) immunizations.2 In 2005, formulations suitable for adolescents and adults (Tdap vaccine) were approved, and an additional 1-time booster dose is recommended.3