Pregnant women who received the H1N1 influenza vaccine during the 2009 pandemic were less likely to have premature babies, and their babies weighed more on average.

Influenza infection during pregnancy is associated with adverse infant outcomes such as preterm birth. Emory researchers from the Rollins School of Public Health, in a joint study with Kaiser Permanente of Georgia and the Mid-Atlantic States, evaluated the effectiveness of the H1N1 influenza vaccine in pregnant women against adverse infant outcomes during the 2009 pandemic. They compared birth outcomes among pregnant women who received the vaccine to those among pregnant women who were not vaccinated.

The researchers used de-identified electronic medical records for 3,327 women enrolled in Kaiser Permanente managed care organization sites between April 2009 and April 2010. The study looked at whether women got the H1N1 influenza vaccine during pregnancy and their birth outcomes such as premature birth and birth weight. Overall findings showed that vaccinated mothers were less likely to deliver their babies prematurely. On average, infants of vaccinated mothers also weighed more at birth than infants born to unvaccinated mothers.

"Our findings confirm the importance of receiving the influenza vaccine during pregnancy in order to protect the infant’s health," explains Jennifer Richards, MPH, first author of the study. "Previous studies have shown that seasonal influenza vaccination may prevent preterm birth. This study shows that moms who were vaccinated during the H1N1 pandemic were less likely to have premature babies."

Influenza infection is especially dangerous for pregnant women. It increases risk of adverse infant outcomes, and of complications such as hospitalization for flu. During the 2009 H1N1 influenza pandemic, pregnant women in the U.S. experienced higher influenza-associated morbidity and mortality in comparison to the general population. Getting the flu vaccine during pregnancy can not only help to prevent infection for the mother, but studies have shown that it also protects the fetus and infant after birth.

"There is always an understandable heightened sense of caution by pregnant women," explains senior study author Saad B. Omer, PhD, assistant professor of global health at Rollins and an affiliate investigator at Kaiser Permanente Georgia. "Getting vaccinated has proven to be the best protection. Our study supports the U.S. policy to prioritize pregnant moms to receive the influenza vaccine."