University of Calgary researchers have found a positive connection between the annual flu shot and preventing stroke.
The study, which is getting international attention, took a decade of health record data in Alberta and looked at the risk of stroke after getting vaccinated against influenza.
“Across the study we did see a lower risk of stroke in that six-month time period post-influenza vaccination,” study author Dr. Jessalyn Holodinsky told Global News.
The latest research builds on existing scientific knowledge of a connection between an influenza infection and stroke.
“There’s a longstanding history between infections and stroke — upper respiratory tract infections are associated with stroke — so it was sort of natural to start to look at this,” Dr. Michael Hill said.
“In addition, there’s a relationship between influenza and myocardial infarction – heart attacks – and so drawing the links in with stroke was a natural next step.”
Hill called it a “definitive study” and anticipated another one to follow.
The research was published in The Lancet Public Health, a prestigious scientific journal.
Holodinsky said the quality and depth of the data set the team was looking at produced some surprising results in the connection between the flu shot and stroke prevention.
“What I was surprised by was the magnitude. I wasn’t surprised that the effect existed but I was surprised by how strong the effect was and especially that the effect existed for all adults,” she said, noting there was a protective effect regardless of existence of chronic conditions.
“We all seem to benefit from this.”
Hill said the connection between stroke or heart attack and upper respiratory infections like influenza or strep could also apply to COVID-19.
“We know pathologically that some of the mechanisms of stroke are related to specific bacteria or viruses that will infect not only your lungs or your bronchioles, but also plaque in the carotid artery for example. So there are some mechanistic reasons to believe that preventing upper respiratory infections will also reduce your risk of ischemic events like stroke,” he said.
For Holodinsky, the message from the data is clear.
“What a great added bonus here too, that (the flu vaccine) might be influencing your cardiovascular risk profile as well,” she said. “I think this is great messaging for the public, especially with influenza vaccination season upon us right now, to go out and consider getting your influenza vaccination.”
Albertans are going out to get vaccinated for influenza, but at a slower pace than in previous years. In the first week shots were publicly available, nearly 300,000 doses were administered.
“That’s about 6.5 per cent of the population. When comparing that to last year, we were over 10 per cent already at that same timeframe,” AHS Calgary Zone medical officer of health Dr. Karla Gustafson said. “So definitely some room for improvement with vaccine uptake.”
Last flu season, 467,521 doses went into Albertans’ arms.
One Calgary pharmacist said this early flu season is the busiest she’s had in recent memory, crediting awareness of vaccinations against COVID-19.
“Everybody is really excited to get the flu shot,” Laila Kharoub of Sirocco Pharmacy told Global News. “The COVID vaccination got people to be more aware of the importance of the flu shot. So it’s been a really busy year for us.”
Kharoub’s pharmacy has been seeing between 70 and 80 customers per day to get a flu shot since they became widely available on Oct. 17, and more people in a wider age range than previous years.
Hill said he is personally more concerned about influenza this fall and winter than COVID, because of how the flu hit other countries earlier this year.
“They had quite a go of it in Australia and the southern hemisphere, and usually when it’s bad in the southern hemisphere, it’s then bad in the northern hemisphere,” Hill said.
“It’s not a perfect relationship but I think we could be in for quite a hit this winter.”
As of Oct. 16, Alberta had 47 active lab-confirmed cases of influenza A and influenza B. The previous week, there was only 28 cases of influenza. Through all of this flu season there were 138 total cases, with 21 people hospitalized and four in ICU.
The medical officer of health said vaccination can lighten the load on already stressed hospitals across the province.
“We do want to have that capacity in the health system to help people when they need it most and I’m sure that no one wants to be hospitalized with a respiratory virus,” she said. “So vaccine really is your best protection against that.”
Gustafson understands any weariness around getting another vaccine, but said there’s no better time to get a shot.
“With flu here and on the rise, it’s really important that people do take that bit of effort to get out and get a vaccine for influenza.”
–with files from Su-Ling Goh and Craig Momney, Global News