Pregnant women given the Tdap vaccine produced similar levels of antibodies against the disease in a small pilot study.

Among the 28 women in the study, there was a nonsignificant difference in the median-fold concentration of most pertussis-specific antigens in a group of 17 pregnant women and 11 nonpregnant controls, reported Lisa Gray, MD, of the University of Rochester Medical Center in NY, and colleagues.

There was one significant difference in median-fold antibody concentration for fimbriae 2,3, with values significantly lower among the pregnant women compared with controls (P=0.048 for IgG levels and P=0.027 for IgA levels), they reported in a presentation at the Society for Reproductive Investigation annual meeting.

However, this may have been due to the two vaccine types used in the study — one contained fimbriae (Adacel) and one did not (Boostrix). There were three participants in the study for whom vaccine type was unknown.

“Even though testing of baseline characteristics did not suggest a systematic difference in vaccine type administered by pregnancy status, that statistical analysis is not robust,” Gray explained. “Given the small sample size of the study, these results are very sensitive to small changes in data, and that may explain these findings.”

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