Tdap Vaccination During Pregnancy Appears Safe

A small study suggests that pertussis vaccination during pregnancy increases antibody concentration in infants without increasing the rate of adverse reactions.

Vaccinating women against pertussis during pregnancy is safe for both mothers and babies, the results of a recent study indicate. The study, published in the May 7, 2014, issue of the Journal of the American Medical Association, also found that immunization during pregnancy with the tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis (Tdap) vaccine resulted in significantly higher concentrations of antibodies to all vaccine antigens in infants during their first 2 months of life.

The study began before the 2012 recommendation from the Advisory Committee on Immunization Practices that all women should receive the Tdap vaccine during every pregnancy and evaluated the safety and immunogenicity of administering the Tdap vaccine to expectant mothers during their third trimester. From October 2008 through May 2012, women at 30 to 32 weeks’ gestation were randomized to receive the Tdap vaccine or placebo. After giving birth, women who received the placebo were given the vaccine and those who had already received the vaccine were given the placebo. Adverse reactions and immunogenicity were recorded and compared between the 2 groups of pregnant women and with an age-matched group of non-pregnant women who were vaccinated with Tdap.

The results indicated that adverse reactions from vaccination were similar in the 2 groups of women. The proportion of women who experienced injection site reactions did not significantly differ between the groups and no serious adverse reactions were associated with Tdap vaccination. Systemic symptoms occurred in 36.4% of women vaccinated before birth, 73.3% of women vaccinated after birth, and 53.1% of non-pregnant women. Non-serious adverse events occurred in 63.6% of women vaccinated during pregnancy, 73.3% of women vaccinated after pregnancy, and 28.1% of non-pregnant women. Growth and development were similar in both groups of infants, and no cases of pertussis occurred during the follow-up period.

The results also suggest that Tdap vaccination during pregnancy is effective. Women who received the vaccination during pregnancy had significantly higher concentrations of pertussis antibodies when they gave birth than did those who were vaccinated after giving birth. In addition, infants born to mothers who were vaccinated during pregnancy had significantly higher concentrations of pertussis antibodies at birth and at the age of 2 months. Tdap vaccination during pregnancy also did not alter infant responses to the diphtheria and tetanus toxoids and acellular pertussis (DTaP) vaccine. When infants included in the study were aged 13 months and had received 4 doses of the DTaP vaccine, concentrations of pertussis antibodies were not significantly different between the infant groups.

Although the results of the trial are potentially important in learning more about preventing pertussis, only 48 pregnant and 32 non-pregnant women were included in the study. This small sample size “lacks the statistical power to detect potential differences between groups for safety and immunogenicity,” note Natalia Jiménez-Truque, MSCI, PhD, and Kathryn M. Edwards, MD, in an accompanying editorial. Additional cohort or surveillance studies conducted with large sample sizes are needed to assess the effects of Tdap vaccination during pregnancy.