Maternal vaccination against seasonal flu may benefit fetus

Infants born to mothers who were vaccinated during pregnancy had higher birth weights and less prematurity, data from three studies presented yesterday at the 47th Annual Meeting of the Infectious Diseases Society of America indicated.

Researchers from Emory University in Atlanta identified 4,168 women who gave birth between June 2004 and September 2006, of whom 15% had been vaccinated against influenza during pregnancy.

Infants born at the peak of influenza season whose mothers had been vaccinated had a 70% overall lower chance of being born prematurely. These infants were also 70% less likely to be small for gestational age, said Saad B. Omer, MPH, PhD, an assistant professor of global health at Emory who presented the data.

In two other studies presented by Mark C. Steinhoff, MD, of Cincinnati Children’s Medical Center, data showed that infants born to women who received the influenza vaccine weighed an average of nearly half a pound more than infants born to women who had not been vaccinated. Also, 25% of the infants born to unvaccinated mothers showed serological evidence of influenza infection compared with only 10% in the vaccinated group.

Steinhoff’s group examined data from 340 Bangladeshi women who had randomly been assigned to either inactivated influenza or pneumococcal vaccine groups.

About 25% of the infants had an influenza infection in the first six months of life, data indicated. This is important to note Steinhoff said, because respiratory viruses circulate for longer periods in the tropics, a situation unlike the one in the United States where influenza rates have been reported in the 10% range and usually have a seasonal peak.

“When you prevent influenza in pregnant women it not only benefits the mother; we think this shows it also benefits the fetus,” Steinhoff said, adding that he expects other larger studies examining influenza in tropical settings.

Omer said the data presented at the meeting makes a strong case for maternal vaccination against influenza. He said that current flu vaccination rates among pregnant women “are dismal” at about 15%. – by Colleen Zacharyczuk

For more information:

Omer S. Impact of maternal immunization against influenza and birth weight.

Steinhoff MC. Influenza immunization in pregnancy and birth weights: observations from a randomized controlled trial in S. Asia.

Henkle E. Serologically defined influenza infection in early infancy in South Asia.

All presented at the Infectious Diseases Society of America Meeting. Oct. 29-Nov. 1, 2009. Philadelphia.