During the study, the researchers observed a 63 percent reduction in proven influenza illness among infants born to vaccinated mothers while the number of serious respiratory illnesses to both mothers and infants dropped by 36 percent.
The study is the first to show that the inactivated influenza vaccine provides protection to both mother and newborn.
The inactivated influenza vaccine (the flu shot) is not licensed for infants younger than six months. The alternative nasal flu vaccine is not available for children under age 2.
"Even though there is no flu vaccine for these children, our study shows that a newborn's risk of infection can be greatly reduced by vaccinating mom during pregnancy. It's a two for one benefit," said Mark Steinhoff, MD, the study's senior author and professor in the Bloomberg School's Department of International Health.
"Infants under six months have the highest rates of hospitalization from influenza among children in the U.S. These admission rates are higher than those for the elderly and other high-risk adult groups," he added.
The study was conducted in Bangladesh in collaboration with researchers from the International Centre for Diarrheal Disease Research (ICDDR,B).
Researchers studied 340 mothers and their infants as part of the larger Mother's Gift vaccine evaluation study. The mothers were randomly selected to receive either flu vaccine or pneumococcal vaccine.
"Pregnant woman should be encouraged to be vaccinated for the flu to protect their infants and themselves," said Steinhoff.
The findings were presented during the National Vaccine Advisory Committee meeting in Washington, D.C. on September 17 and will be published in the October 9 issue of the New England Journal of Medicine.