Positive birth outcomes for flu vaccine during pregnancy

An Aussie study has found reassuring evidence of flu vaccine safety during pregnancy, but some mums still have concerns

The cohort study led by the Menzies School of Health Research enrolled 7,126 women who gave birth to a single infant between 2012 and 2014.

In this group there were 2,429 women who had flu vaccine during their pregnancy (34%), while the remainder (66%) did not.

Mean maternal age of participants at birth of infant was 31.7 years, and most mothers who received the flu vaccine did so in the second trimester (51%).

The study published in Vaccine found there were no statisfically significant differences between vaccinated and unvaccinated mothers in relation to weeks’ gestation at birth of the infant: 38.7 versus 38.8 weeks respectively (p=0.051).

Researchers found a non-significant difference of 15g in the point of estimate of birthweight between infants born to vaccinated mothers (3337g) compared with infants born to unvaccinated mothers (3352g). Mean birthweight across the whole cohort was 3347g.

“Our results showed no clinically significant difference in infant birthweight or gestational age at birth of the infant for women who received an influenza vaccination during any trimester of pregnancy compared with unvaccinated mothers,” says the lead author, Menzies PhD student Lisa McHugh.

She says the findings support the current recommendation in Australia to vaccinate all women who are pregnant during the influenza season.

“The reason flu vaccination is recommended in pregnancy by the World Health Organization and other expert groups is because pregnant women are at higher risk of severe illness if they do acquire influenza infection when pregnant,” she says.

“This is due to reduced immunity or if the pregnant woman has a co-morbidity or risk factor such as diabetes or a history of respiratory illness like asthma or bronchitis.”

Researchers hope the study results will reassure pregnant women and healthcare providers that vaccination is the best course of action to prevent influenza infection during pregnancy.

Uptake in this cohort is currently lower than it should be, says chief investigator, Menzies research fellow and chair of the Australian Technical Advisory Group on Immunisation, Professor Ross Andrews.

He says the results reveal some concerns prevail surrounding the safety of the flu vaccine during pregnancy.

“Monitoring safety, uptake and effectiveness is critical for any vaccine program but particularly for vaccines given in pregnancy,” says Professor Andrews.

“In our study, only one in three women had a flu vaccine during their pregnancy, despite the recommendations.”

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