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Maternal Tdap Vaccination during Pregnancy: Impact on Infant Anti-pertussis Antibody Concentrations by Maternal Pertussis Priming Series.

BACKGROUND
Acellular pertussis (aP) vaccines replaced whole cell pertussis (wP) vaccines for the U.S. childhood primary series in 1997. As women primed with aP vaccines enter childbearing age, protection of infants through Tdap (tetanus toxoid, reduced diphtheria toxoid and acellular pertussis) vaccination during pregnancy may be impacted.


METHODS
Term infants born to women vaccinated with Tdap during pregnancy were included. Geometric mean concentrations (GMC) of pertussis-specific IgG antibodies (IU/mL) in cord blood of infants born to women born after 1997 (aP-primed) were compared with those born to women born before 1992 (wP-primed).


RESULTS
253 and 506 infants born to aP- and wP-primed women, respectively, were included. Compared with wP-primed women, aP-primed women were younger, more likely to be Hispanic or non-Hispanic Black, and had lower birthweight infants (p < 0.01 for all). Antibodies against pertussis toxin (PT) and filamentous hemagglutinin (FHA) were lower among infants born to aP-primed versus wP-primed women (PT: 17.3 vs. 36.4, GMC ratio 0.475 (95% Confidence Interval [CI], 0.408-0.552); FHA: 104.6 vs. 121.4, GMC ratio 0.861 (95% CI, 0.776-0.958)). No differences were observed for anti-fimbriae or anti-pertactin antibodies.


CONCLUSIONS
Transplacental anti-pertussis antibody concentrations in infants of women vaccinated with Tdap during pregnancy differed by type of childhood vaccine the woman received. Notably, anti-PT antibody levels, considered most important in preventing severe infant disease, were lower in infants born to aP- vs. wP-primed women. Maternal Tdap vaccination may confer less protection against pertussis in young infants born to aP-primed than those born to wP-primed women.