F2 and pertussis: Most studies suggest that Tdap vaccination early in the third trimester results in the highest anti–pertussis toxin (anti-PT) IgG antibody levels at birth,4,5,6,7 while a Swiss study favored second-trimester vaccination, potentially due to a longer time interval between Tdap vaccination and delivery.10,11 Recently, it was estimated that a period of 7.5 weeks or more before delivery optimizes antibody transfer.5 Tdap vaccination before 24 weeks’ gestation may therefore be particularly relevant for preterm offspring, the group most vulnerable for severe pertussis.