Safety of inadvertent anthrax vaccination during pregnancy: An analysis of birth defects in the U.S. military population, 2003–2010

Abstract Background Anthrax vaccine adsorbed (AVA) vaccination is compulsory for United States military servicemembers with operational indicators. As the number of female military servicemembers has increased, so has the chance of inadvertent AVA vaccination during pregnancy. Building upon past analyses assessing AVA vaccination during pregnancy and birth defects risk, this study sought to determine if inadvertent AVA vaccination during pregnancy is significantly associated with risk of birth defects after adjusting for other potential risk factors. Methods The study population included 126,839 liveborn infants in the Department of Defense Birth and Infant Health Registry (2003–2010). Mothers were categorized by AVA vaccination exposure timing in relation to pregnancy. Infant medical records were assessed for birth defect diagnoses within the first year of life. Multivariable logistic regression was used to calculate odds ratios (ORs) and 95% confidence intervals (CIs). Results Infants of first trimester AVA vaccinated mothers versus receipt at any other time point (OR, 1.10; 95% CI, 0.93–1.29) were not at higher odds of birth defects in adjusted models. Infants of mothers vaccinated prepregnancy versus postpregnancy had a 1.11 (95% CI, 1.01–1.22) higher odds of having a birth defect. Vaccination postpregnancy versus never vaccinated revealed a 10% lower odds of birth defects (OR, 0.90; 95% CI, 0.83–0.99). Conclusions No strong associations between inadvertent AVA vaccination during pregnancy and birth defects risk were observed. Marginal associations between prepregnancy vaccination or never vaccinated women and birth defects risk was observed when compared to postpregnancy vaccination. These findings may be due to self-selection and/or reverse causation bias when assessing comparisons with postpregnancy vaccination, and a “healthy worker” effect when assessing comparisons with women never vaccinated.