Concomitant Tdap, Influenza Vaccines Safe in Pregnancy

Diana Swift

October 14, 2015

Coadministration of tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis (Tdap) and influenza vaccines in pregnant women does not appear to raise the risk for medically attended adverse acute outcomes or birth outcomes compared with sequential vaccination, according to a large retrospective cohort study published online October 5 in Obstetrics and Gynecology.

Lakshmi Sukumaran, MD, MPH, a pediatric infectious diseases specialist at the Immunization Safety Office, Centers for Disease Control and Prevention, Atlanta, Georgia, and colleagues studied data from pregnant women in the Vaccine Safety Datalink from January 1, 2007, to November 15, 2013. The Vaccine Safety Datalink is a collaborative project between the Centers for Disease Control and Prevention's Immunization Safety Office and nine healthcare organizations.

The authors compared medically attended acute events such as fever, as well as adverse birth outcomes, such as preterm delivery, low birth weight, and small for gestational age, in women receiving concomitant or sequential Tdap and influenza vaccination.

At baseline, the two cohorts were similar in maternal age, enrollment in a healthcare plan before pregnancy, prenatal care use, comorbidities, and receipt of other vaccinations during pregnancy.

The researchers identified 633,542 singleton pregnancies during the study period, of which 443,774 resulted in live births. Among 36,844 pregnancies in which Tdap and influenza vaccines were administered, immunization was administered concomitantly in 8464 (23%) pregnancies, and sequentially in 28,380 (77%) pregnancies.

Gestational age at Tdap and influenza vaccination was 25 weeks (range, 1 - 40 weeks) for same-day immunization; in different-day immunization, it was 27 weeks (range 1 - 41 weeks) for the Tdap vaccine and 19 weeks (range, 1 - 40 weeks) for the influenza vaccine (P < .001). In women vaccinated on different days, the mean number of days between Tdap and influenza vaccines was 94 days (median, 84 days).

Acute adverse events after vaccination were rare, and there was no statistically significant increased risk for fever or any other medically attended acute adverse events between the two groups. Analyzing women at 20 weeks' or more gestation during periods of influenza vaccine administration, the investigators found no differences in preterm delivery or low-birth-weight or small-for-gestational-age neonates between the two groups.

There were no cases of Arthus reaction or Guillain-Barré syndrome, nor was there was any interaction between acute adverse events and gestational age at Tdap vaccination.

The authors note, however, that "the rarity of adverse events in our cohort may also be related to differences in the immune response that occur during pregnancy to protect the fetus. Such differences may result in pregnant women being less reactogenic in response to vaccines."

These results are similar to those from randomized studies in nonpregnant women that showed no difference in acute events after concomitant and sequential Tdap and influenza vaccination.

"Our findings should be reassuring to health care providers and pregnant women, especially for women who are later in their pregnancy during months of influenza vaccine administration and are most likely to receive concomitant vaccination," Dr Sukumaran and colleagues write.

Dr Sukumaran has received research support from the National Institute of Allergy and Infectious Diseases. One coauthor has received research support from GlaxoSmithKline, Sanofi Pasteur, Merck & Co, Pfizer, Nuron Biotech, MedImmune, Novartis, and Protein Science. Another coauthor has received research support from GlaxoSmithKline and Pfizer. The other coauthors have disclosed no relevant financial relationships.

Obstet Gynecol. Published online October 5, 2015. Abstract