"The development of a child inside the mother affects that child during its entire life, and low birth weight has lifelong health implications for a child," said Mark Steinhoff from Cincinnati Children's Hospital in the US.
"The overall positive effect of performing these vaccinations – which is not expensive – is quite significant," Steinhoff added.
For the study, 3,693 mothers (between the ages of 15 and 40) were recruited and randomised into two different annual research groups (or cohorts) from April 2011 through September 2013.
In cohort 1, compared to the placebo group, influenza-like illness was reduced by 9 percent in pre- and post-partum mothers who received vaccine. In cohort 2, flu-like illness was reduced by 36 per cent. This placed the average flu reduction rate for both groups of vaccinated mothers at 19 per cent.
For infants, lab-confirmed flu infections in cohort 1 decreased 16 per cent in babies with vaccinated mothers. In cohort 2 they decreased by 60 per cent – putting the average rate of reduction for both cohorts at 30 per cent.
As for birth weight, flu immunisations in pregnant mothers reduced the rate of low birth weight (less than 2,500 grams/5.5 pounds) by 15 per cent in cohort 1 and by 15 per cent in cohort 2 (average 15 per cent for both groups).