Flu Vaccines for Moms Increase Birth Weights of Their Children

Tuesday, February 21, 2012

An international research team led by scientists from Cincinnati Children’s Hospital Medical Center has discovered that birth weights increase for babies of women who are immunized for the flu.

The study, led by Mark Steinhoff, MD, director of the Center for Global Child Health at Cincinnati Children’s, is published in the February issue of the Canadian Medical Association Journal.

“What makes these findings important is that for the first time, we have proven that beyond protecting moms and their babies from influenza, the flu vaccine also increases the birth weight of the infants, giving them a better chance at a healthier life,” says Dr. Steinhoff.

This study is part of the Mother’s Gift project, which took place in Bangladesh under Dr. Steinhoff’s oversight. Part of the Mother’s Gift findings were published in the New England Journal of Medicine in 2008 and showed that influenza vaccine not only prevents pregnant women from getting influenza but also protects their infants. It was the first study to demonstrate that the inactivated influenza vaccine provides such dual protection.

The new data is further evidence of the effect of the flu vaccine, which is recommended for pregnant women in the United States but is not licensed for infants younger than 6 months of age.

The birth weight work was part of the prospective, blinded, randomized Mother’s Gift trial carried out from August 2004 to November 2005 involving 340 pregnant urban Bangladeshi women. The study considered time intervals of high and low flu virus circulation and found when there was no flu circulation there were similar birth weights among both the control group and the vaccinated group.

However, during the interval of flu circulation, when the flu vaccine prevented illness, the mean birth weight of infants in the influenza vaccine group was nearly seven ounces, or 7 percent greater. In addition, the proportion of “small for gestation age” babies was more than halved from 41 percent in the control group to 17 percent in the flu vaccine group.

These findings have been corroborated in retrospective studies in the United States, Canada, and the United Kingdom. Taken together they show that influenza vaccine in pregnancy benefits the mother, the fetus, and the young infant, according to Dr. Steinhoff.

In addition to the Center for Global Child Health at Cincinnati Children’s, others participating in the work included the International Centre for Diarrhoeal Disease Research, Dhaka, Bangladesh; the Rollins School of Public Health, Emory University, Atlanta; and the Centers for Disease Control and Prevention, Atlanta.

Following the Mother's Gift study, Cincinnati Children's received a grant for more than $10 million from the Bill and Melinda Gates Foundation to more broadly evaluate influenza vaccine in a region of Nepal. This four-year project began in April last year in a region of Nepal typical of much of South Asia in that access to medical care is limited. A project immunizing women during pregnancy would, however, be feasible.

The researchers intend to enroll 3,600 women, half of whom would receive the vaccine and half placebo. The scientists will evaluate the rates of influenza among mothers and their infants. They also will analyze birth weight and gestational age.

About Cincinnati Children’s

Cincinnati Children’s Hospital Medical Center ranks third in the nation among all Honor Roll hospitals in U.S. News and World Report’s 2011 Best Children’s Hospitals ranking. It is ranked #1 for gastroenterology and in the top 10 for all pediatric specialties – a distinction shared by only two other pediatric hospitals in the United States. Cincinnati Children’s is one of the top two recipients of pediatric research grants from the National Institutes of Health. It is internationally recognized for improving child health and transforming delivery of care through fully integrated, globally recognized research, education and innovation. Additional information can be found at

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