Study finds flu vaccine during pregnancy does not adversely affect early childhood health

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Researchers at IWK Health, in partnership with leading vaccine and infectious diseases researchers, have found that maternal influenza vaccination during pregnancy is not significantly associated with an increased risk of adverse early childhood health outcomes. The study published in the Journal of the American Medical Association looked at all live births in Nova Scotia over four flu seasons, between October 1 2010 and March 31 2014, and then followed them until they reached an average age of three and a half years.

Dr. Azar Mehrabadi, photo by Ryan Wilson IWK

“High-quality evidence from clinical trials shows that getting an influenza vaccine in pregnancy both protects the pregnant person and the newborn baby from getting the flu,” says Dr. Azar Mehrabadi, lead author and perinatal epidemiologist at IWK Health. “Despite this, pregnant people have hesitated to get vaccinated, citing safety concerns.”

Influenza viruses cause substantial morbidity and mortality in pregnant women and newborns worldwide every year, with higher incidence during pandemics. In 2012 the World Health Organization recommended that countries prioritize pregnant women for influenza vaccination to reduce disease incidence in these vulnerable populations.

Dr. Deshayne Fell

“We assessed immune-related pediatric health outcomes such as rates of asthma, ear infections, respiratory infections, and other infections and did not find any association with influenza vaccination during pregnancy,” says the study’s principal investigator, Dr. Deshayne Fell, associate professor at the University of Ottawa and scientist at the CHEO Research Institute, a pediatric hospital and research centre in Ottawa. “Moreover, there was also no association with other serious health conditions such as pediatric cancer or sensory disorders, and no difference in need to access urgent health care in emergency departments or hospitals between children born to mothers who received the flu shot during pregnancy and those born to mothers who did not.”

The study measured children’s health outcomes from emergency department and hospitalization databases.

“As pandemic-related public health restrictions are reduced, we expect influenza illness will likely re-emerge this coming flu season,” says Mehrabadi. “Influenza vaccination is one of the best tools we have to protect pregnant individuals and newborn babies from influenza illness and the associated serious complications that can affect this vulnerable population.”

While many studies have shown that influenza vaccination during pregnancy is safe and does not increase the chances of having pregnancy complications or adverse birth outcomes, there are only a few studies evaluating longer-term health outcomes in children whose mothers were vaccinated against influenza during their pregnancy.

“Infants under six months of age can have serious complications if they get the flu, but they are not eligible to become vaccinated against the flu during the first six months of life,” says Fell. “One of the major benefits of vaccinating pregnant people, therefore, is the ability to protect newborn babies from getting the flu after they are born, since they receive the mother’s protective antibodies that are produced following flu vaccination during pregnancy.”

The study was funded by the Canadian Institutes of Health Research.