Flu vaccine ‘safe in any trimester of pregnancy’

The influenza vaccine is safe to receive at any stage during pregnancy, the results of a large Australian study have determined.

The study, published in the journal Vaccine, found that birth outcomes, specifically birth weight and weeks' gestation of the infant at birth, are not affected by the influenza vaccine during any trimester of pregnancy.

Researchers at the Australian National University in Canberra, and colleagues conducted a nested retrospective cohort study of "FluMum" participants to investigate the effects of influenza vaccination during any trimester of pregnancy on infant birth weight and weeks' gestation at birth of the infant. “Vaccine safety and effectiveness are key concerns and influencers of uptake for both vaccine providers and families,” noted the authors.

Over 7,000 women gave birth during the study, 34% of whom had received the influenza vaccine during pregnancy. The researchers found no statistically significant differences between infants born to vaccinated vs unvaccinated women. Infants born to vaccinated women had a mean gestation of 38.7 weeks vs 38.8 weeks in the unvaccinated group. Mean birth weight of infants born to vaccinated women was marginally lower; 3337 g vs 3352 g in the unvaccinated group.

In addition, most of the infants (83%) were born during the Australian influenza season, and no relationship between season of birth and either low birth weights or preterm births were observed.

Of the 1,705 women with an identified influenza vaccination date, 14% received the vaccine in the first trimester, 51% received the vaccine in the second trimester, and 35% received the vaccine in the third trimester.

The researchers called the results of the study “reassuring” and urged women to consider flu vaccination, especially if suffering from comorbidities or other risk factors.

“Physicians can reassure women who will be pregnant during the flu season that there is no increased risk of having a preterm baby or low birth weight baby if they get an influenza vaccine during any stage of their pregnancy. This is especially important for pregnant women who have comorbidities or other risk factors which may affect their immunity and capacity to cope with an infectious disease in pregnancy such as influenza,” they commented.
The World Health Organisation recommends that expectant mothers have the flu vaccine during pregnancy, as flu can lead to serious complications for mothers and their unborn infants.

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