Flu shots help keep unborn babies at healthy weight

Immunity altered by pregnancy: study

Flu shots during pregnancy protect babies from being born underweight, new research published in Canada’s top medical journal suggests.

Small- for- gestational- age babies have an increased risk of lifelong health consequences when they’re older, including obesity, heart disease and diabetes.

The new study, appearing in this week’s issue of the Canadian Medical Association Journal, suggests that when a mother gets the flu during pregnancy, it affects an unborn baby’s fetal growth.

The study was conducted by a team of U. S. and Bangladeshi researchers. In all, 340 healthy pregnant women in Bangladesh were put into two groups: one received an influenza vaccine, and the second received the pneumococcal vaccine as a “control.”

Researchers compared the weight of babies born in two periods: during flu season and outside flu season.

When the flu virus was dormant, there was no difference between the two groups of mothers in terms of the percentage of babies born to them which were small for their gestational age.

But when flu was circulating, not only was there less flu- like disease among the mothers and babies who had received the flu shot, the babies born to the mothers vaccinated against flu weighed, on average, 200 grams more.

“That’s a big difference in mean birth weight,” said lead author Dr. Mark Steinhoff, a professor of pediatrics at Cincinnati Children’s Hospital Medical Center.

Overall, the percentage of small- for- gestational- age babies was lower in the flu vaccine group than in the control group ( 25.9 per cent versus 44.8 per cent).

In total, 336 babies were delivered; 327 were included in the analysis. Three stillbirths occurred among the mothers vaccinated against flu, but researchers said the difference isn’t statistically significant and that the stillbirths were due to chance and not the vaccine.

It’s well known that, when there’s a pandemic, pregnant women are highly vulnerable.

DR. MARK STEINHOFF PROFESSOR OF PEDIATRICS, CINCINNATI CHILDREN’S HOSPITAL MEDICAL CENTER

“It’s well known that, when there’s a pandemic, pregnant women are highly vulnerable,” said Steinhoff.

But even in non- pandemic years, Canadian research has shown that pregnant women are at an increased risk of being hospitalized with pneumonia or other flu- related complications. As women get closer to their due dates, their immune systems change, making them more vulnerable to serious illness due to influenza and other infections. That can put stress on the fetus.

Steinhoff’s team estimates vaccinating 10 pregnant women against the flu prevents one small- for- gestational- age baby.

Other research has shown that the rate of premature births is lower among vaccinated mothers.

The Public Health Agency of Canada says expectant mothers, at any stage of pregnancy, should get a flu shot to protect themselves and their babies. The agency says it’s particularly important that women who will be in the later stages of their pregnancies, the second and third trimester, during flu season ( which runs from November to April) are immunized because they face a greater risk of being hospitalized. The highest risk of hospitalization from flu is during the third trimester.