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Evaluating the Flu Shot: A Randomized Controlled Trial of the Influenza Vaccine During Pregnancy

Flu Shot PreparationsAccording to recommendations by both the World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC), pregnant women should receive the inactivated influenza vaccine at the start of the flu season. In the study entitled “Adverse events in pregnant women following administration of trivalent inactivated influenza vaccine and live attenuated influenza vaccine in the Vaccine Adverse Event Reporting System, 1990-2009” as published in the American Journal of Obstetrics & Gynecology, researchers from the CDC and the Food and Drug Administration (FDA) observed no unusual patterns of pregnancy complications or fetal outcomes among women vaccinated with the flu shot during pregnancy, thus confirming the safety of the influenza vaccine for pregnant women.

Until recently, however, little data existed on the effects of maternal influenza infection on fetuses and newborns. A recent study led by Mark C. Steinhoff, MD, of the Bloomberg School of Public Health at Johns Hopkins University as published as “Neonatal outcomes after influenza immunization during pregnancy: A randomized controlled trial” in the April 2012 issue of the Canadian Medical Association Journal sought to determine the effects of the flu on babies born to mothers with the infection as well as to the effectiveness of inactivated influenza and pneumococcal vaccines during pregnancy.

For the study, which was performed from August 2004 through December 2005, 340 pregnant women in Bangladesh received either the inactivated influenza vaccine or the 23-valent pneumococcal polysaccharide vaccine, which was the control group. The researchers then performed an analysis of the outcomes on the babies born following maternal influenza immunization during two periods. The first period was from September 2004 through January 2005 when the influenza virus was not circulating. The second period was from February through October 2005 when the influenza virus was circulating. The researchers assessed gestational age, mean birth weight, and the proportion of infants who were small for gestational age.

During the first period in which the influenza virus was not circulating, there were no differences in the incidence of respiratory illness with fever per 100 person-months among mothers and infants in the two groups. Additionally, the proportion of infants who were small for gestational age and the mean birth weight were similar between groups.

However, during the second period in which the influenza virus was circulating, there was a substantial reduction in the incidence per 100 person-months of respiratory illness with fever among the mothers and infants who had received the influenza vaccine. Even more significantly, the proportion of infants who were small for gestational age was lower in the influenza vaccine group than in the control group. The mean birth weight was also higher among newborns whose mothers received the flu shot during pregnancy than among those who received the control vaccine.

As the researchers conclude, during the times of the year when the influenza virus is circulating, maternal immunization against the flu during pregnancy was associated with a lower proportion of newborns who were small for gestational age and an increase in mean birth weight. In other words, receiving the flu shot during pregnancy and the subsequent prevention of maternal influenza infection can influence intrauterine growth.

Yet another reason to get the flu shot during pregnancy.

References

Neonatal outcomes after influenza immunization during pregnancy: A randomized controlled trial: http://www.ncbi.nlm.nih.gov/pubmed/22353593

Image Credits

Flu Shot Preparations: http://commons.wikimedia.org/wiki/File:US_Navy_021019-N-9593M-007_Flu_shot_preparations.jpg

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