Timing of Prenatal Tdap Immunization and Protection Against Pertussis

Dear Editor—With great interest we read the most recent contribution of Winter et al. reporting on the vaccine effectiveness (VE) of prenatal tetanus, diphtheria, and acellular pertussis (Tdap) immunization in the prevention of pertussis among young infants as compared to postpartum Tdap immunization [1]. Winter et al. reports that the calculated VE of prenatal Tdap immunization in preventing pertussis among infants <8 weeks of age was 85% when Tdap was administered during 27–36 weeks gestation (WG) [1]. Moreover, infants whose mothers received Tdap during 27–36 WG were less likely to have pertussis during the first three months of life as compared to infants born to mothers who received prenatal Tdap outside 27–36 WG [1]. These findings are robust and support the current Centers for Disease Control and Prevention recommendation for the preferential administration of Tdap during 27–36 WG [2]. Interestingly, further subanalysis revealed that infants born to mothers who received Tdap during early third trimester (27–31 WG) had lower odds ratio to have pertussis infection at <8 or ≤12 weeks of age as compared to infants whose mothers received Tdap during 32–36 WG [1]. As the authors state, although the confidence intervals of the odds ratio were wide, these data suggest that early third trimester immunization might be more effective in the prevention of pertussis infection among young infants when compared to immunization beyond 31 WG [1]. The latter finding supports the current data on the effect of timing of prenatal Tdap immunization on pertussis immunity provided to the newborns [3–5]. Abu Raya et al. reported that immunization with Tdap during 27–30+6 WG yielded the highest levels of immunoglobulin G (IgG) to pertussis toxin (PT) and filamentous hemagglutinin (FHA) and the highest avidity of IgG to PT conveyed to the newborn at delivery, as compared to immunization beyond 31 WG [3, 4]. Moreover, Naidu et al. reported that immunization during 28–32 WG provided newborns with the highest levels of IgG to PT, FHA, and pertactin as compared to immunization during 33–36 WG [5]. In response to these findings, some national guidelines have specified their recommendations regarding the preferred timing of prenatal Tdap administration. The Australian National Health and Medical Research Council endorsed Immunization Handbook recommendation states that early third trimester (28–32 WG) is the optimal timing for prenatal Tdap immunization [6]. The study by Winter et al. provides further evidence to support this statement. Maternal Tdap immunization is gaining acceptance among public health policy makers in different countries. However, cases of vaccine failure have been reported among infants born to women immunized with Tdap between 27 and 36 WG [1, 7]. There is a need for more scientific evidence exploring the optimal window for immunization during pregnancy that provides young infants with the highest clinical protection against pertussis. The available immunogenicity and clinical data indicate that early third trimester immunization has the potential to maximize protection against pertussis during early infancy. Thus, efforts should be made to administer Tdap to pregnant women at the earliest opportunity between 27–36 WG. Potential conflicts of interest. Both authors do not have any association that might pose a conflict of interest. Both authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed.

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