Tdap Safe in Pregnancy After Other Recent Tetanus Vaccine

Laurie Barclay, MD

October 21, 2015

Pregnant women given tetanus, diphtheria, and acellular pertussis (Tdap) vaccine had no increase in acute adverse events or adverse birth outcomes associated with receipt of a prior tetanus-containing vaccination within the previous 5 years, according to a retrospective cohort study published October 20 in JAMA.

The Advisory Committee on Immunization Practices recommends that women receive Tdap vaccine during each pregnancy, regardless of prior immunization status, yet safety data in pregnant women were lacking.

"Most safety studies on administering repeated doses of tetanus-containing vaccines are limited to nonpregnant individuals," write Lakshmi Sukumaran, MD, MPH, from the Immunization Safety Office, Centers for Disease Control and Prevention, Atlanta, Georgia, and colleagues. "These studies have shown that intervals less than 5 years between tetanus-containing vaccines can be associated with increased local reactions and fever."

The goal of the current study was to examine whether administration of Tdap vaccine during pregnancy in close intervals to prior tetanus-containing vaccinations was linked to acute adverse events in pregnant women or to adverse birth outcomes. These included maternal fever, allergy, and local reactions, and small for gestational age, preterm delivery, and low birth weight in the neonates.

Using data from seven Vaccine Safety Datalink sites in California, Colorado, Minnesota, Oregon, Washington, and Wisconsin, the investigators identified 29,155 pregnant women aged 14 through 49 years who had documentation of a prior tetanus-containing vaccine and receipt of Tdap during pregnancy. The authors stratified the participants according to the timing of their most recent tetanus-containing vaccine. All pregnancies ended between January 1, 2007, and November 15, 2013.

Compared with women who were vaccinated with Tdap in pregnancy and who had a prior tetanus-containing vaccine more than 5 years before, those who received Tdap in pregnancy after a prior tetanus-containing vaccine less than 2 years before, or 2 to 5 years before, had no statistically significant differences in rates of medically attended acute adverse events or adverse birth outcomes.

"Our findings should reassure patients and clinicians who might be hesitant to give Tdap vaccine to pregnant women who recently received a Tdap or other tetanus-containing vaccination," the study authors write.

Study limitations include limited power for the acute adverse events analysis; exclusion of women with no prior documented tetanus-containing vaccination, allowing for more conservative estimates of risk; potential confounding resulting from differences in the type of vaccine received; and lack of medical chart review.

"One explanation of the apparent paucity of acute adverse events with short tetanus vaccination intervals in our study could be related to shifts in immunological responses that occur during pregnancy," the study authors conclude.

"Future studies are needed to determine if there are differences in other important adverse pregnancy outcomes, such as stillbirth and spontaneous abortion, when Tdap is given in pregnancy in close intervals from prior tetanus-containing vaccines."

The Centers for Disease Control and Prevention and the National Institute of Allergy and Infectious Diseases funded this study. Two of the study authors reported financial disclosures involving GlaxoSmithKline, Pfizer, Sanofi Pasteur, Merck, Nuron Biotech, MedImmune, Novartis, and/or Protein Science. The other authors have disclosed no relevant financial relationships.

JAMA. 2015;314:1581-1587. Abstract

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