The study suggests that unborn babies in Bangladesh benefit from their mother’s flu vaccine, increasing their birth weight by an average of 200g and giving them a better chance of survival.
Published in the Canadian Medical Association Journal, the project was a joint effort by US and Bangladeshi researchers and included 340 healthy pregnant women. The Bill and Melinda Gates Foundation has given a $10 million grant to replicate the study in 3,600 patients in Nepal.
The scientists behind the Bangladesh project say their results suggest flu infection during pregnancy affects foetal growth which can ultimately increase the risk of health problems after birth.
Pregnant women taking part in the study were divided into two groups. One group was given a flu vaccine while the other was given the pneumococcal vaccine as a ‘control’.
The weights of babies born during flu season were compared to those born outside flu season. It was found that outside flu season – when flu infections are very rare – there was no difference between the two groups in terms of the percentage of babies born underweight.
However, during flu season – when flu viruses are in circulation – two clear differences were found. Fewer cases of flu-like illness were recorded in mothers and babies who had been given the flu vaccine. In addition, babies born to mothers immunised against the flu weighed an average of 200g more than those whose mothers had not been vaccinated against flu.
“That’s a big difference in mean birth weight,” lead author Dr. Mark Steinhoff, a professor of pediatrics at Cincinnati Children’s Hospital Medical Center, told Canada.com.
The percentage of ‘small-for-gestational-age’ babies was lower in the flu vaccine group than in the control group – 25.9% compared to 44.8%.
There were three stillbirths among the group vaccinated against flu but Dr Steinhoff said the analysis showed that this is due to chance rather than the vaccine.
Other research has shown that the rate of premature births is lower among vaccinated mothers, and that pregnant women are at an increased risk of being hospitalised with pneumonia or flu-related complications.