Background: The Centers for Disease Control and Prevention recommend Tdap immunization during pregnancy, preferably at 27-36 weeks.
Aim: To ascertain whether there is a preferential period of maternal Tdap immunization during pregnancy that provides the highest concentration of pertussis-specific antibodies to the newborn.
Methods: This prospective study measured pertussis-specific antibodies in paired maternal-cord sera of women immunized with Tdap after the 20th week of their pregnancy (n=61).
Results: The geometric mean concentrations (GMCs) of Immunoglobulin G (IgG) to pertussis toxin (PT) were higher in the newborns’ cord sera when women were immunized at 27-30+6 weeks (n=21) compared with 31-36 weeks (n=30) and > 36 weeks (n=7), 46.04 international units/milliliter (IU/mL) (95% CI, 24.29-87.30) vs. 8.69 IU/mL (95% CI, 3.66-20.63) and 21.12 IU/mL (95% CI, 7.93-56.22), p<0.02, respectively. The umbilical cord GMCs of IgG to filamentous hemagglutinin (FHA) were higher in the newborns’ cord sera when women were immunized at 27-30+6 weeks compared with 31-36 weeks and > 36 weeks, 225.86 IU/mL (95% CI, 182.34- 279.76) vs. 178.31 IU/mL (95% CI, 134.59- 237.03) and 138.03 IU/mL (95% CI, 97.61-195.16), p<0.02, respectively.
Conclusions: Immunization of pregnant women with Tdap between 27-30+6 weeks was associated with the highest umbilical cord GMCs of IgG to PT and FHA compared with immunization beyond 31 weeks gestation. Further research should be conducted to reaffirm these finding in order to promote an optimal pertussis controlling policy.
