Importance The United States has experienced a nationwide resurgence of pertussis since
the mid-1970s, despite high estimated vaccine coverage. Short-lived immunity induced by
diphtheria-tetanus–acellular pertussis (DTaP) vaccines in young children is widely believed
to be responsible for this growing burden, but the duration of protection conferred by DTaP
vaccines remains incompletely quantified. Objective To assess the duration of immunity and
the effectiveness of DTaP vaccines in US children. Design, Setting, and Participants A …