Annual flu shot can greatly reduce risk of stroke in adults, Canadian researchers say

Getting the flu shot can significantly reduce the chances of having a stroke, according to a new Canadian study.

"We found that those individuals actually had a lower risk of stroke than individuals who didn't receive a flu shot or at other times of the year outside of that six-month-post window," said Dr. Jessalyn Holodinsky, the study's first author and a post doctoral fellow at the University of Calgary's Cumming School of Medicine.

In a research paper published Wednesday in the medical journal The Lancet Public Health, the team examined the health of more than four million adult Albertans of all ages and health backgrounds over a 10-year span.

"That's over four million people - and it's actually over 30 million person years of follow up when you're following that many people for that length of time, so it was a lot of data we had to work with," Dr. Holodinsky said.

The research uses by far the largest data set applied to the relationship between influenza vaccination and cardiovascular health researchers say, and while the link to stroke is new, it also supports previous studies that looked at heart attack risk.

It also sheds further light on a phenomenon long observed in hospitals.

"(When there is a) peak of influenza in the community, about three or four weeks later we get a peak of stroke admitted to hospital," said Dr. Michael Hill, one of the study's co-authors. "So there's a relationship between upper respiratory infections and vascular events like ischemic-stroke."

The research did not specifically examine why getting immunized against the flu significantly lowered the risk of stroke across ages and health histories, but the working hypothesis is that fewer flu cases means less stroke risk. In this understanding, vaccination is simply the reason for the reduced cases.

Roughly 30 per cent of people get the flu shot each year in Alberta, while roughly 3,300 Albertans suffer a stroke each year according to data published by AHS.

While more research is needed, the study's authors believe getting a flu shot may one day be a recognized pillar of cardiovascular health advice, along with good diet, exercise and not smoking.

"Interestingly, there's a cost benefit associated with that - if you vaccinate working age adults, the economy benefits. Because more people are at work. And they're not sick," Dr. Hill said.