When a pregnant woman gets a flu shot, she is also protecting her baby, according to a new study.

Researchers from Johns Hopkins University found that infants born to mothers who had been vaccinated had a 63 percent lower chance of getting the flu. There were also 36 percent fewer cases of serious respiratory problems in the babies.

A news release did not say what the general rate of infection is for newborns, so it is not clear how many cases of the flu this prevents. But a researcher said that the rate of hospitalization for the flu is higher among children under 6 months old than for any other group, including the elderly.

The flu shot is not approved for infants younger than 6 months, and nasal vaccines can't be given until age 2.

Researchers said that about 15 percent of pregnant women get inoculated, though advice generally is for them to do so.

"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 senior author Dr. Mark Steinhoff.

The study was conducted in Bangladesh and will be published in the Oct. 9 issue of the New England Journal of Medicine.