In Reply As noted by Abu-Raya and Giles, preterm infants are at an increased risk of severe pertussis. We agree that in the maternal vaccination era, the most appropriate role for pertussis vaccine without diphtheria and tetanus (aP) at birth is when the mother did not receive tetanus toxoid, reduced diphtheria toxoid, and pertussis antigen content (Tdap) during pregnancy or her infant was born prematurely.1 However, our study1 cannot inform use in premature infants because our protocol precluded enrollment of infants born prior to 36 weeks’ gestation and required administration of vaccine before 120 hours after birth, whereas if aP vaccine was given to a preterm infant only when stable medically, this would often be at more than 120 hours after birth.