Researchers Uncover Possible Link Between Flu Vaccine and Stroke Protection

A new study from Spain suggests that a flu shot lowers the risk of stroke, apart from any protection against the flu the vaccine provides. Researchers observed a 12% lower risk of getting a stroke in the vaccinated population after confounding factors were adjusted.

Wolter Kluwer Health, Inc. published the article on behalf of the American Academy of Neurology in Neurology early September.

The Potential Connection Between Flu Vaccines and Strokes

A stroke occurs when the blood supply to the brain is cut off, causing damage to neuronal cells that, in turn, affects physiological functions in the body. Different types of strokes can occur, while the most common is ischemic stroke, which accounts for 87% of all strokes. 

Many accepted factors account for approximately 80% of stroke risk, including high blood pressure, diabetes, sedentary behavior, and smoking. Most of these exert long-term effects, and scientists are working to understand what factors might underlie short-term risk. 

According to a recent study, having the flu may increase the chances of getting an ischemic stroke by 40%, uncovering the possible association between the flu and stroke.

The biological mechanism is hypothesized to be related to the systemic inflammation caused by the infection, which can result in the atheroma plaque rupturing and precipitating the occurrence of vascular atherothrombotic events, according to Professor Francisco Jose de Abajo from the Department of Biomedical Sciences at the University of Alcalá. 

Encouraging At-Risk Populations to Vaccinate

If influenza-like illnesses can potentially trigger a stroke, could a flu vaccine have protective effects for stroke?

Using a Spanish healthcare database, the researchers performed a nested-case control study, with a total of 3.8 million patients recruited. The study included patients between 40 and 99 years old because ischemic stroke in a younger population is rare. After a follow-up period of 14 years, results showed that 41.4% of individuals that received a flu shot had a stroke, compared to 40.5% that had not.

However, adjusting for various possible confounding factors such as hypertension, smoking, obesity, or hypercholesterolemia changed the result. The research team also adjusted for pharmacological treatments, such as using drugs for cardiovascular and metabolic diseases. After accounting for these confounding factors, individuals receiving an influenza vaccine were 12% less likely to have a stroke than those unvaccinated.

Although the research is observational, which means the researchers could not determine the causation between flu vaccines and stroke protection, it does provide evidence of an association. Furthermore, the research highlighted the extravascular benefit, which encouraged the public, especially those with cardiovascular risk factors, to vaccinate against influenza. The challenge is flu vaccination coverage in most countries is below the WHO recommended target. Further studies are needed to help raise public awareness of the benefits of vaccination and increase coverage as part of preventive public health measures.

Author

Nai Ye Yeat