Babies are much less likely to get the flu during their first six months of life, if their moms get flu vaccinations while pregnant, a U.S. study said Tuesday.

Infants six months and younger, whose mothers were vaccinated when pregnant, had a 70 per cent reduction in laboratory-confirmed flu cases and an 80 percent reduction in flu-related hospitalisations, compared with babies whose moms weren’t immunised, according to the study published online in the U.S. journal Pediatrics.

"Babies cannot be immunised during their first six months, so they must rely on others for protection from the flu during that time,” said lead author Julie Shakib, assistant professor of pediatrics at the University of Utah School of Medicine.”When pregnant women get the flu vaccine there are clear benefits for their infants.”

In the new study, Shakib and colleagues examined more than 245,000 de-identified health records of pregnant women and more than 249,000 infant records for nine flu seasons from December 2005 through March 2014.

About 10 per cent of the women–23,383–reported being vaccinated while pregnant compared with 222,003 who said they were not vaccinated, they found.

Over the study’s course, laboratory-confirmed flu cases were reported among 658 infants. Of these cases, 638, or 97 per cent, occurred in babies whose moms were not immunised. A total of 151 of the 658 infants were hospitalised, with 148 being born to non-immunised pregnant women.