With flu season rapidly approaching, there may be an additional benefit to getting your flu shot: a lower risk of stroke. A study conducted in Spain and published in Neurology showed that out of 86,000 older adults, those who got their annual flu shot were less likely to suffer an ischemic stroke over the next year. (Most strokes that occur are ischemic, meaning they are caused by a blood clot that blocks the flow of blood and oxygen to the brain.)
While the risk reduction linked to the flu shot was moderate — vaccinated people were 12 percent less likely to suffer a stroke compared to their unvaccinated counterparts — senior researcher Dr. Francisco Jose de Abajo, MD, MPH, PhD, believes this research could have far-reaching benefits.
Many people suffer a stroke each year, and many of them could get the influenza vaccine and potentially reduce their risk; still, “to determine whether this is due to a protective effect of the vaccine itself or to other factors, more research is needed,” de Abajo explained in a press release.
Linking the Flu Shot to Lower Stroke Risk
For the study, researchers used a healthcare database in Spain to identify people who were at least 40 years of age and had a first stroke over a 14-year period. Each person who had a stroke was compared to five people of the same age and sex who’d never had one. There were a total of 14,322 people who had a stroke and 71,610 people who did not have a stroke.
Next, the researchers recorded the number of people who had received the flu vaccine at least 14 days before their stroke. They also recorded the number of people who did not have a stroke for at least two weeks after receiving the vaccine, and the number of people who had no flu shot but did have a stroke.
About 41 percent of people who received a flu shot had a stroke, compared to 40.5 percent of those who did not have a stroke. After researchers adjusted their findings in favor of those factors, they concluded that those who received a flu shot were 12 percent less likely to have a stroke than those who did not get vaccinated.
Why might this be? Previous research has shown that the flu (and also COVID!) can increase a person’s stroke risk. Serious illness causes stress on the body, and that stress raises the likelihood that a stroke will occur. “Infections are well-known triggers,” Babak Navi, MD, told the American Heart Association in 2020. Thus, getting the flu vaccine may prevent serious illness, which in turn may reduce stroke risk.
The Study’s Limitations
As with any study, it’s important to take this one with a grain of salt. Since the study was observational, it does not definitively prove that getting your flu shot reduces the risk of stroke — it only shows an association. Other factors not measured or accounted for in the study could also affect a person’s risk. For instance, those who got the shot tended to be older and have other high-risk conditions, such as high blood pressure or cholesterol, which could increase their stroke probability.
De Abajo noted that it’s difficult to account for all the differences between those who get a yearly flu shot and those who do not. People who get their recommended vaccinations are probably more likely to be health-conscious in other ways too, such as healthy eating or taking prescribed medications for high blood pressure or cholesterol. These qualities may lower their risk of stroke further.
Study authors did account for the differences they could, including body weight, smoking, and chronic health conditions. With these considerations, the link between flu vaccination and lower stroke risk remained.
The Bottom Line
Despite the study’s limitations, these findings present a hopeful possibility: A number of strokes could be averted if the flu shot provides even a minimal protective effect. “These results are yet another reason for people to get their yearly flu shot, especially if they are at an increased risk of stroke,” de Abajo said. “To be able to reduce your risk of stroke by taking such a simple action is very compelling.”
While flu vaccination may not prevent infection entirely, it is proven to reduce the severity of the flu. People with a history of stroke, or risk factors for it, have an increased chance of experiencing severe flu complications — so it’s all the more important for at-risk individuals to get vaccinated. “We hope that studies such as ours will help to enhance public awareness of the benefits of being vaccinated,” de Abajo said.
An added bonus: Getting your flu vaccine may also cut your COVID risk.