Flu Shot During Pregnancy May Halve Stillbirth Risk

A new study suggests that seasonal trivalent influenza vaccination (TIV) during pregnancy is associated with a significant reduction in stillbirths.

Researchers at the University of Western Australia (UWA; Crawley, Australia) and Emory University (Atlanta, GA, USA) conducted a large, population-based study to evaluate the incidence of stillbirth following seasonal TIV. Probabilistic linking of perinatal and maternal vaccination records was used to establish a cohort of 58,008 births occurring between April 2012 and December 2013. Regression models were used to calculate adjusted hazard ratios (HRs) for maternal smoking, indigenous status, and propensity for vaccination in vaccinated and unvaccinated mothers.

In all, 5,076 (8.8%) pregnant women received trivalent TIV, and 377 stillbirths occurred among the 58,008 mother and baby pairs. There were 5 and 3 stillbirths per 100,000 pregnancy-days among unvaccinated and vaccinated women, respectively. After adjustment, the results showed that stillbirth was 51% less likely among vaccinated women, with the largest relative reduction observed for births occurring just after influenza season. The study was published on March 30, 2016, in Clinical Infectious Diseases.

“These results may be useful for communicating the potential benefits of seasonal influenza vaccination to pregnant mothers and their providers,” concluded lead author Annette Regan, MPH, of UWA and the Western Australia department of health. “Given the growing body of evidence supporting the health benefits to mother and infant, concerted efforts are needed to improve seasonal influenza vaccine coverage among pregnant women.”

Changes in the immune system, heart, and lungs during pregnancy make pregnant women more prone to severe illness from flu, as well as to hospitalizations and even death. Getting the flu during pregnancy also raises the risks of pregnancy complications, including premature labor and delivery. Studies have shown that vaccinating a pregnant woman can pass antibodies on to the baby that will protect against flu for six months after birth.

Influenza spreads around the world in a yearly outbreak cycle, resulting in about three to five million cases of severe illness and about 250,000-500,000 annual deaths. In the Northern and Southern parts of the world outbreaks occur mainly in winter, while in areas around the equator outbreaks may occur at any time of the year. Death occurs mostly in the young, the old, and those with co-morbidities. In the 20th century three influenza pandemics, resulting in millions of deaths, occurred: Spanish influenza in 1918, Asian influenza in 1958, and Hong Kong influenza in 1968.

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University of Western Australia
Emory University