In Monday's issue of the Canadian Medical Association Journal, doctors reviewed rates of seasonal flu vaccination for 12,223 women in Nova Scotia who gave birth to to a liveborn or stillborn infant between 2010 and 2012.
During the 2009 H1N1 pandemic, government data suggested 64 per cent of pregnant women received the flu vaccine. At the time, pregnant women were one of the priority groups to be vaccinated first.
In the latest study, the vaccination rate among pregnant women fell to 16 per cent.
Since 2007, the study's authors said evidence from studies showing benefits of influenza vaccination for both mothers and babies was compelling enough for advisory boards in Canada to recommend routine flu shots for all pregnant women.
"However, despite these recommendations, the rates of seasonal influenza vaccination in our study were disappointingly low," Alexandra Legge, a fourth-year medical student at Dalhousie University in Halifax, and her co-authors concluded.
"Our attention must now turn toward efforts to improve these vaccination rates."
In other studies, pregnant women cite concern about vaccine safety as the top reason for refusing the vaccine. Legge noted that at the recommendation of their care provider, women will often agree to a vaccination despite their concerns.
"Our population-based study showed a reduced likelihood of preterm birth and low birth weight among infants whose mothers received the seasonal influenza vaccine during pregnancy. Our findings add to the existing body of evidence that show that seasonal influenza vaccination during pregnancy not only offers maternal benefits, but may also provide both prenatal benefits to the fetus and postnatal protection to the infant," the study's authors said.
The researchers did not have information about ethnic background or education levels, which could also play a role in the association between getting a flu shot and pregnancy outcomes.
They also didn't have the date women were vaccinated to look for any effects by trimester.
When the researchers analyzed the data, excluding deliveries during the peak vaccination period of November and December, they did not detect any differences.
There was no direct funding for the study. Some of the authors have financial ties to vaccine manufacturers.