Flu vaccine decreases risk of stroke: Alberta study

The flu vaccine may help prevent stroke among adults, according to a University of Calgary (UCalgary) study released Wednesday.

The records of more than four million Albertans were evaluated by UCalgary researchers at the Cummings School of Medicine over a nine-year period.

According to the study first published in The Lancet Public Health, this is “the largest study of influenza vaccination and stroke risk to date.”

The university “strongly” recommends vaccination against influenza, including those with heart disease.

Dr. Michael Hill, a physician and principal investigator on the study, said there is literature going back 25 years showing respiratory infections can be linked to strokes.

“The flu shot is known to reduce the risk of heart attack and hospitalization for people with heart disease. We wanted to find out whether the vaccine has the same protective qualities for those at risk of stroke,” said Hill in a statement.

“Our findings show the risk of stroke is lower among people who have recently received a flu shot. This was true for all adults, not just those at high risk of having a stroke.”

Dr. Michael Hill, a professor at the Cumming School of Medicine in the Department of Clinical Neurosciences and Radiology, poses for a photo in Calgary. Hill is a neurologist with the Calgary Stroke Program of Alberta Health Services and a researcher at the University of Calgary’s Hotchkiss Brain Institute (HBI). (Riley Brandt, University of Calgary photo)

The study’s data come from the Alberta Health Insurance Plan, and several factors were used, including age, reduced blood clot usage, and risk factors including “chronic health conditions.”

Hill says anything that would prevent a respiratory infection would lower the risk.

“Why does a heart attack or a stroke occur? What are the triggers? It turns out one of the triggers is recent upper respiratory infections and so the natural thing to ask is ‘what if you protect against that?’ And the one area we chose to look at was influenza,” Hill said.

Dr. Jessalyn Holodinsky, a stroke epidemiologist and first author of the study, says vaccination may be a “viable public health strategy to prevent stroke.”

“What we’ve found in about the six-month period after receiving an influenza vaccination, individuals seemed to be protected against having a stroke. The risk of having a stroke was reduced by just over 20 per cent and that was across individuals of all adult ages, both men and women,” Holodinsky said.

Dr. Jessalyn Holodinsky, a PhD, postdoctoral scholar at the Cumming School of Medicine poses for a photo in Calgary. Holodinsky is the first author in a study that shows a new benefit to the annual influenza shot. (Original shot by Adrian Shellard, University of Calgary photo)

She says the reduction in the risk of a stroke was 23 per cent overall. The risk reduction in men was 28 per cent, but in women it was only 17.

“That’s likely stemming from males being at higher risk of stroke, to begin with,” Holodinsky said. “Importantly, everyone (even the healthy) benefited to some degree.”

The UCalgary study adds to the research already conducted by the Calgary Stroke Program, which is a collaboration between UCalgary through the Hotchkiss Brain Institute, and AHS at the Foothills Medical Centre.

The Canadian Institute for Health Information says stroke is the third leading cause of death in Canada, and more than 62,000 strokes occur each year.