Protection Against Pertussis From Maternal Tdap Vaccination During Pregnancy Before and After Infant DTaP Vaccination in 148 981 Newborns Followed From Birth Until 12 Months of Age

12-mo Follow-up (Total Pertussis Cases = 103)
No. of Pertussis Cases (Rate per 100 000 Person-Years)VE, % (95% CI)P
No Maternal Tdap Maternal Tdap
Maternal Tdap during pregnancy (8+ days before birth)a
 0 DTaP doses (birth until day 7 after the first DTaPdose)31 (177.2)2 (14.8)87.9 (41.4 to 97.5).009
 Protected by 1 DTaP doseb23 (170.3)5 (43.2)81.4 (42.5 to 94.0).004
 Protected by 2 DTaP dosesb12 (88.5)8 (72.8)6.4 (−165.1 to 66.9).901
 Protected by 3 DTaP dosesb14 (48.7)7 (32.1)65.9 (4.5 to 87.8).041
Maternal Tdap before pregnancy89 (89.4)14 (42.4)55.6 (20.1 to 75.4).007
Maternal Tdap after pregnancy80 (72.1)23 (106.2)24.1 (−28.5 to 55.1).305
  • a We calculated the VE of maternal Tdap vaccination during pregnancy after each infant DTaP vaccine dose based on a Cox regression model that included an 8-level variable created by interacting a 2-level Tdap variable (0 = unvaccinated during pregnancy, 1 = vaccinated during pregnancy 8+ days before birth) and a 4-level DTaP variable (0, 1, 2, or 3 doses). The model was stratified on the year and month of birth of the infant and included covariates to adjust for sex, race, delivery hospital, and maternal Tdap before and after pregnancy. We used contrast statements to estimate the VE of maternal Tdap vaccination during pregnancy after each infant DTaP dose. Case counts do not include 1 infant whose mother received the Tdap vaccine 1 to 7 days before birth because the VE estimates do not include infants whose mothers were vaccinated 1 to 7 days before birth as either vaccinated or unvaccinated during pregnancy; there were too few infants in this group to give a meaningful result, so the 1 case where this occurred is not included.

  • b Protected by DTaP dose: from day 8 after the DTaP dose until day 7 after the next dose.