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    Tdap vaccine: No connection found to microcephaly

    According to a research letter in JAMA, the tetanus, diphtheria, and acellular pertussis (Tdap) vaccine may not be linked to an increased risk of microcephaly or other structural birth defects.

    Researchers looked at singleton live births from January 2007 to September 2013 at 7 Vaccine Safety Datalink sites in Northern California, Southern California, Colorado, Minnesota, Oregon, Washington, and Wisconsin. They compared the prevalence of structural birth defects among infants born to women who had received the Tdap vaccine during pregnancy and those born to women who were unvaccinated. Pregnancies were found in electronic healthcare data using a validated algorithm. Each woman involved had to be continuously insured from 6 months prior to her last menstrual period until 6 weeks postpartum and had to have 1 or more outpatient visits to ensure that all diagnoses were accounted for. The infants had to have their birth weight and gestational age data recorded and they had to be insured for 4 months of their first year with 1 or more outpatient visits. Any infants with exposures known to increase the risk of structural defect, such as use of teratogenic medication, were excluded from the study.

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    Three vaccine windows were examined: less than 14 weeks’ gestation, the current recommendation of 27 to 36 weeks’ gestation, and any other gestational week. Diagnostic codes were used to identify any structural effect, major structural effect, or microcephaly.

    The study covered 324,463 live singleton births. The maternal Tdap vaccine was not significantly associated with increased risk of microcephaly when it vaccine was given at less than 14 weeks’ gestation (n = 3321; adjusted prevalence ratio [APR], 0.96 [95% confidence interval {CI}, 0.36-2.58]). Similar results were seen with vaccination given between 27 and 37 weeks (n = 20568; APR, 1.01 [95% CI, 0.63-1.61]) or any other week of gestation (n = 41 654; APR, 0.86 [95% CI,0.60-1.24]). Analyses for any structural defect and selected structural defects were similar.

    Investigators concluded that the Tdap vaccine continues to be safe in pregnancy and they support the current recommendation for routine Tdap vaccination during pregnancy.

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    Miranda Hester
    Ms. Hester is Content Specialist with Contemporary OB/GYN and Contemporary Pediatrics.
    Judith M. Orvos, ELS
    Judith M. Orvos, ELS, is a a BELS-certified medical writer and editor and an editorial consultant for Contemporary OB/GYN.


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