A major new Ottawa study should reduce the anxiety that many pregnant women experience when confronted with the question of whether to get a flu shot.
The study, published in a leading medical journal, the BMJ , tracked disease and hospitalization rates for 104,000 children born in Ontario between November 2009 and October 2010 — during the swine flu (H1N1) pandemic.
It found that the 31,295 children born to mothers who received the flu vaccine were just as healthy as the 79,954 children born to mothers who didn’t take it.
Researchers used the province’s health databases to link birth registry information with hospital records. They wanted to understand whether a mother’s vaccination played any role in the health outcomes of children during the first five years of their lives.
“This is a large study and it clearly shows that there were no harmful effects on the longer-term health of children when a pregnant woman got the flu shot,” said CHEO Research Institute scientist, Dr. Deshayne Fell, a senior author of the study.
“Influenza vaccination during pregnancy is — by all available evidence — safe for mothers and their offspring,” said Fell, an assistant professor at uOttawa’s School of Epidemiology and Public Health.
In Canada, only about 20 per cent of pregnant women opt for a flu shot; research shows many avoid being vaccinated because of safety concerns.
But the flu vaccine offers protection against influenza both to a mother and her baby, Fell said, since maternal antibodies cross the placenta. Those antibodies confer protection — passive immunity — during the first six months of a child’s life.
Health statistics show that flu-related death rates among children are highest for those under six months when an infant’s immune system is still being developed.
“This is really important because we know that getting the flu shot in pregnancy reduces the women’s chance of getting the flu — and they’re a high-risk group,” said Fell. “But it also can prevent influenza in babies in the first few months of life, which is when they’re particularly vulnerable but can’t be vaccinated.”
Infants cannot be vaccinated until they reach six months of age.
“I think most people, when they think of getting the flu shot, they think of preventing the flu in themselves — and that’s already a compelling enough reason,” she said. “But the big thing here is that it has the additional bonus of protecting the babies.”
In the study, researchers found that the children of vaccinated mothers did not have higher rates of death, cancer, serious infections, chronic diseases, sensory disorders, hospital admissions or emergency room visits. The same cohort had a slightly higher rate of asthma, and a slightly lower rate of serious gastrointestinal infections.
The study’s authors could find no biological mechanism to explain the weak association between a mother’s immunization and a child’s asthma. (Researchers did not assess children for autism because there’s no available database to which birth records can be linked.)
According to the Public Health Agency of Canada, an average of 3,500 deaths a year can be attributed to the flu in this country. Most of those deaths occur among the elderly and infirm.
In Canada, about 36 per cent of adults receive the flu vaccine in any given year.
Fell said the new study is important because it adds to existing scientific literature that shows the flu vaccine has no negative short-term health effects on mothers or their infants: “I think it adds to the evidence, which has been growing rapidly in the last five years, that there’s no harmful effects to getting vaccinated against influenza — either for the mothers or babies.”
Copyright Postmedia Network Inc., 2019
