Concomitant Flu and Pertussis Vaccination in Pregnancy Shows No Increased Risk

A new population-based cohort study has found no increased risk of adverse pregnancy, birth, or neonatal outcomes when influenza and pertussis-containing vaccines are administered on the same day during pregnancy compared to receiving the pertussis vaccine alone.

The study, conducted by researchers from the Sydney Children’s Hospitals Network, analyzed perinatal, immunization, and hospitalization data for singleton pregnancies in New South Wales, Australia, occurring in 2021 and 2022. It compared 6,959 pregnant women who received both influenza and pertussis vaccines concomitantly (on the same day) at 20 weeks’ gestation or later with 6,959 matched women who received only the pertussis vaccine. Matching was based on vaccination date, gestational age at vaccination, and maternal age.

The mean maternal age at delivery was 31.7 years across both groups. Among women who received both vaccines on the same day, 3.8% of pregnancies ended in preterm birth, compared to 4.4% in the pertussis-only group. For live, full-term births, 8.8% of infants in the concomitant vaccine group were small for gestational age, versus 9.9% in the control group. Low birth weight occurred in 1.7% of infants in the concomitant group and 1.6% in the pertussis-only group.

The authors concluded that no association was found between concomitant influenza- and pertussis-containing vaccine administration during pregnancy and an increased rate of adverse pregnancy, birth, or neonatal outcomes compared with pertussis vaccination alone.

These findings align with current public health recommendations from major health organizations, which advise that pregnant individuals receive both the inactivated influenza vaccine and the tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis (Tdap) vaccine during each pregnancy to protect both mother and newborn. The influenza vaccine is recommended during any trimester, while Tdap is advised between 27 and 36 weeks of gestation to maximize passive antibody transfer to the fetus.

Administering both vaccines during pregnancy helps reduce the risk of flu-related complications in pregnant people, who are at higher risk for severe illness due to changes in immune, heart, and lung functions. It also protects newborns from pertussis in the first months of life, before they can receive their own vaccinations, a period when whooping cough can be life-threatening.

The study’s design, which used a large matched cohort from real-world data, strengthens the reliability of its conclusions. By controlling for key variables such as timing of vaccination and maternal age, the researchers minimized potential confounding factors that could influence birth outcomes.

While the study provides robust evidence supporting the safety of same-day administration of these two vaccines in pregnancy, the researchers note that ongoing surveillance is important to continue monitoring maternal and infant health outcomes as vaccine formulations and populations evolve.

Healthcare providers can use these findings to reassure patients that receiving both the flu and pertussis vaccines during the same visit is a safe and effective way to ensure timely protection against both diseases, without increasing the risk of adverse birth or neonatal outcomes.