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Influenza vaccination during pregnancy may lead to improved birth outcomes
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Canadian researchers reported that influenza vaccination during pregnancy was associated with improved neonatal outcomes, including a lower risk for preterm birth and low birth weight.
“Our findings add to the existing body of evidence showing that seasonal influenza vaccination during pregnancy not only offers maternal benefits, but may also provide both prenatal benefits to the fetus and postnatal protection to the infant through transplacental antibodies,” the researchers wrote in CMAJ.
Alexandra Legge, a fourth-year medical student at Dalhousie University in Halifax, Nova Scotia, Canada, and colleagues used data from the Nova Scotia Atlee Perinatal Database to examine maternal vaccination rates and neonatal outcomes in all women who gave birth in Nova Scotia between Nov. 1, 2010, and March 31, 2012 (n=12,223).
Alexandra Legge
Results indicated that 16% of the cohort was vaccinated against influenza during pregnancy, a coverage rate the researchers described as “disappointingly low.”
Certain maternal characteristics were found to be predictors of influenza vaccine receipt. Women residing in rural areas (adjusted OR=1.18; 95% CI, 1.06-1.32) and women with medical comorbidities (adjusted OR=1.22; 95% CI, 1.08-1.38) were more likely to receive the influenza vaccine during pregnancy. Single women (adjusted OR=0.83; 95% CI, 0.07-0.94), multiparous women (adjusted OR=0.87; 95% CI, 0.78-0.96) and women who smoked during pregnancy (adjusted OR=0.81; 95% CI, 0.71-0.94) were all less likely to have been vaccinated.
However, infants of vaccinated women had lower odds of preterm birth (OR=0.75; 95% CI, 0.6-0.94) and having low birth weight (OR=0.73; 95% CI, 0.56-0.95).
The researchers wrote that maternal infection has been cited as a risk factor for preterm birth in previous research, and “by averting maternal infection, the vaccine may exert a protective effect on the fetus by avoiding the associated inflammatory response that may trigger premature [labor].”
As the evidence of the protective effect of influenza vaccination accumulates, efforts should be focused on increasing vaccination coverage, they said.
“Thus far, the evidence suggests that rates are highest when pregnant women receive a recommendation for influenza vaccination from their antenatal care provider, who can then offer the vaccine in the same care setting,” the researchers wrote. “Future research should include comparisons of vaccination rates between different care models. Once the care models with optimal vaccine uptake are identified, research will be needed into how best to incorporate them into practice.”
Alexandra Legge can be reached at alex.legge@dal.ca.
Disclosure: Study researcher Jeffrey Scott, MD, has financial relationships with Sanofi-Pasteur. Shelly McNeil, MD, has conducted clinical trials for manufacturers of influenza vaccines, including Sanofi, GlaxoSmithKline and Novartis, and has received research funding from Sanofi and GlaxoSmithKline.
Perspective
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Carol J. Baker, MD
The investigation by Legge and colleagues sought to determine influenza vaccine uptake in pregnant women in Nova Scotia during two seasons following the 2009 H1N1 pandemic when a 64% uptake was recorded. In this well-designed study using a validated perinatal database containing all maternal and neonatal outcomes for the province, only 16% of 12,173 women received influenza vaccine during the second or third trimesters, despite the Canadian recommendation since 2007 that all pregnant women receive influenza vaccine. Confirming previous reports from the US, influenza vaccination at least 15 days before delivery was protective against preterm delivery (<37 weeks) and low birth weight. Although this study did not follow the newborns, several other reports have indicated that influenza vaccine during pregnancy protects not only against preterm birth and low birth weight but also against all febrile respiratory disease and laboratory-confirmed influenza in their offspring during the first months of life.
This study adds to the enlarging body of knowledge that vaccinating pregnant women reduces infant, as well as maternal, morbidity through transport of protective levels of maternal antibodies against influenza (Blanchard-Rohner G. Pediatr Infect Dis J. 2013;32:1374-1380.). Despite this information, pregnant women are not receiving the vaccine and one can only surmise this primarily results from failure of obstetrical providers to recommend vaccination, the single most important reason women do not get vaccinated. What we are lacking is a strong recommendation from the obstetrical provider and easy access to vaccination. The past decade has witnessed publication of numerous studies demonstrating that influenza vaccine is safe for the mother and fetus and that it provides substantial benefit to each patient. It is a shame that a gap for delivering this clearly effective intervention should exist for these vulnerable populations even in resource-rich settings.
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