Tdap Vaccine

Pregnancy

Maternal Tdap evidence includes observational cohorts, a Vaccine Safety Datalink live-birth study, passive reporting, and reviews of primary studies. In a retrospective cohort of 145,883 active-duty pregnancies, 1,272 first-trimester exposures and 9,438 exposures at weeks 27 to 36 were observed; neither exposure timing was associated with spontaneous abortion, preeclampsia, or preterm labor. Among 117,724 liveborn infants, first-trimester exposure was not associated with birth defects, growth problems, preterm birth, or low birth weight. Shakib et al. studied 138 exposed pregnancies and 552 controls, with 63% of exposed participants vaccinated in the first trimester; the small study found no greater incidence of spontaneous or elective abortion and no significant differences in preterm delivery, gestational age, or birth weight. DeSilva et al. examined 324,463 live births and found no association with selected structural birth defects, including microcephaly; Kerr et al. studied 2,357 exposed pregnancies and found no evidence of appreciable risk for selected major malformations. These studies do not assess every pregnancy outcome and cannot rule out every rare event. Greenberg et al. studied 118,211 pregnancies and found no association between Tdap exposure and chorioamnionitis, preterm birth, or adverse infant outcomes; the authors note that administrative codes for chorioamnionitis lack specificity, and several disclosed unrelated industry research support or roles. A 2025 meta-analysis of seven randomized trials and 10 case-control studies estimated 85% effectiveness against infant pertussis before 3 months of age and found no statistically significant association with serious adverse events in the pooled infant or maternal analyses. Hsiao et al. studied 263,809 full-term infants and estimated effectiveness of 96.0% during the first 2 months and 55.8% through the first year; the cohort is observational and includes one Sanofi-affiliated author. Fan et al. analyzed passive VAERS reports from 2005 to 2024, identifying 870 pregnancy-related reports among 20,358 Tdap submissions and disproportionality signals including stillbirth, preterm delivery, and fetal death. The authors explicitly called for validation in active surveillance; a passive-report signal does not estimate incidence or establish causation. CDC’s 2 Dec 2025 page predates that paper and said VAERS had not found signals among pregnant women or their babies. Evidence on timing differs by national program; these timing windows do not establish that earlier administration causes harm.

Breastfeeding

LactMed states that breastfeeding is not a contraindication to Tdap and describes anti-pertussis antibodies in milk after vaccination. It says antibodies may survive infant digestion, while published results conflict on whether breastfeeding adds protection beyond vaccination during pregnancy. Portillo et al. (2024) developed and applied an assay to measure pertussis, tetanus, and diphtheria antibodies in serum and breast milk, including IgA and IgG responses after postpartum Tdap. The study measured immune markers, not infant pertussis illness or clinical protection. Its Methods and Fig. 4 caption give conflicting counts for two-week milk samples, so the draft does not rely on that disputed count. Palmsten et al. (online 6 Sep 2026) examined infant growth and healthcare use after Tdap during lactation; no associations were observed in the eligible lactating subgroups (3,034 for growth and 3,191 for healthcare use). The cohort did not assess every possible infant outcome and disclosed Sanofi support and Sanofi-employed authors. Both U.S. product labels state that milk excretion and effects on breastfed infants or milk production have not been assessed; this is an information gap, not evidence of demonstrated harm.

What was tested

Pregnancy evidence includes retrospective cohorts, linked birth-outcome records, a Vaccine Safety Datalink study, a meta-analysis of randomized and case-control evidence, and a passive VAERS disproportionality analysis. The outcomes included spontaneous abortion, preeclampsia, preterm birth, selected birth defects, stillbirth, newborn growth, infant pertussis, and adverse infant outcomes. The Fan paper analyzed report disproportionality, not incidence or causality. Breastfeeding evidence includes milk antibody measurement after postpartum vaccination and a cohort of infant growth and healthcare use after maternal vaccination while lactating; it does not yet establish whether breast-milk antibodies add clinical infant protection beyond placental antibody transfer. The Portillo paper has inconsistent two-week sample counts between its Methods and figure caption, so that count is not used.