Flu vaccine given to women during pregnancy keeps infants out of the hospital

Infants born to women who received influenza vaccine during pregnancy were hospitalized at a lower rate than infants born to unvaccinated mothers, according to preliminary results of an ongoing study by researchers at Yale School of Medicine. The team presented the study October 29 at the 47th annual meeting of the Infectious Diseases Society of America in Philadelphia.

Influenza is a major cause of serious respiratory disease in pregnant women and of hospitalization in infants. Although the flu vaccine is recommended for all pregnant women and children, no vaccine is approved for infants less than six months of age. Preventive strategies for this age group include general infection control and vaccination of those coming in close contact with them. Few studies have examined the effectiveness of the flu vaccine during pregnancy.

Led by Marietta Vázquez, M.D., assistant professor of pediatrics at Yale School of Medicine, this new study is a case-control trial of the effectiveness of vaccinating pregnant women to prevent hospitalization of their infants. During nine flu seasons from 2000 to 2009, Vázquez and colleagues identified and tracked over 350 mothers and infants from 0 to 12 months of age who were hospitalized at Yale-New Haven Hospital. They compared 157 infants hospitalized due to influenza to 230 influenza-negative infants matched by age and date of hospitalization. The team interviewed parents to determine risk factors for influenza and reviewed medical records of both infants and their mothers to determine rates of vaccination with the influenza vaccine.

"We found that vaccinating mothers during pregnancy was 80 percent effective in preventing hospitalization due to influenza in their infants during the first year of life and 89 percent effective in preventing hospitalization in infants under six months of age," said Vázquez.

"These results not only have a positive impact on the health of susceptible infants, but also may be very cost effective, as it involves one vaccine providing protection to two individuals," Vázquez added. "The findings may also help establish public health policy, increase awareness of the importance of influenza vaccination during pregnancy, and even help to overcome barriers to vaccination."

Other authors on the abstract include Isaac Benowitz, Daina Esposito, Kristina DePeau, Richard A. Martinello, M.D. and Eugene D. Shapiro, M.D.

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November 2, 2009