番茄社区

MONTREAL -- Pregnant women given the tetanus, diphtheria, and acellular pertussis (Tdap) vaccine produced similar levels of antibodies against the disease as a nonpregnant control group, according to a small pilot study presented here.

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 , of the University of Rochester Medical Center in N.Y., 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."

Gray's group looked at a prospective cohort of of women, ages 18-45, who received Tdap vaccination. Those with immunologic/hematologic disease, immunosuppression, or recent blood product use were excluded from the study. Pregnant women were excluded if they had multifetal gestation, anemia, or gestational age outside of 26-36 weeks.

The authors measured IgA and IgG the change in antibody levels from day 0 (prevaccination) to day 28 following vaccination. They developed a pertussis-specific assay measuring IgA and IgG responses to filamentous hemagglutinin, pertussis toxin, pertactin, and fimbriae.

When analyzing response by vaccine type, and not pregnancy status, results were mostly similar, they reported, but added that they noted differences in fold-changes for pertactin by vaccine type, but characterized the explanation for this as "unknown."

The CDC's (ACIP) currently recommends during their third trimester of every pregnancy. But limited actually data exist on the safety and efficacy of this vaccine for pregnant women.

Gray told 番茄社区 that the ACIP recommendation is based on only a few smaller studies. While these data are reassuring, on the safety of multiple doses of Tdap vaccine (such as for women with closely spaced, repeat pregnancies) have been conducted on nonpregnant participants.

She added that there are alterations in the immunologic system in pregnancy and it is not known if pregnant women generate the same immune response to vaccination, as pregnant women are typically excluded from large scale vaccine trials.

"Inferences of efficacy are made based on higher neonatal antibody levels in infants born to vaccinated mothers but the true 'protectiveness' is unknown," Gray said. "I think it is important to increase the body of data regarding safety and efficacy of vaccination in pregnancy as immunization programs are important to global health improvement efforts."

Gray said that an expanded sample size would improve confidence in these results, and that they planned to analyze additional samples in storage after further validation of their assay. She added that while fetal safety concerns, even when there is no reason to suspect harm, prevent researchers from including pregnant women in larger scale vaccine trials, she would like to see that practice changed in order to better study the clinical efficacy in the obstetric population.

"Efforts are underway to encourage this practice," she noted.