Cardiovascular diseases (CVD) are the leading cause of death worldwide, with 14 million deaths per year attributable to a stroke (a type of CVD), according to the Non-Communicable Disease Alliance. Respiratory infections (for example, infections with Mycoplasma pneumoniae, Chlamydia pneumoniae, and influenza viruses) are associated with stroke. However, research into the protective effect of influenza vaccination against stroke has previously generated mixed results. A recent study published in the Lancet Public Health by Holodinsky and colleagues sought to examine the association between influenza vaccination and stroke, finding that individuals recently immunized against influenza had a lower risk of stroke.

A stroke is a life-threatening condition in which the blood supply to part of the brain is cut off. Its major risk factors include high blood pressure, diabetes, heart and blood vessel diseases, smoking, older age, and being of female sex. Individuals from low- to middle-income countries are disproportionately affected, where the prevalence of risk factors is rising and there are major challenges to effective prevention interventions and treatment.

In the study published by Holodinksy and colleagues, cox regression models were used to assess the risk of any stroke in people with and without recent (<182 days) influenza vaccination. Any stroke was defined as an acute ischemic stroke, intracerebral hemorrhage, subarachnoid hemorrhage, or transient ischemic attack. The study included 4,141,209 adults registered under the Alberta provincial health-care system in Canada between 2009 and 2018. During this period, 42.73% of individuals had received at least one vaccination, with 38,126 stroke events recorded. It was found that recent influenza vaccination significantly reduced the risk of stroke by 22.5% among people who had been recently vaccinated against influenza compared with those who had not. This trend was observed across all stroke types.

There are several proposed mechanisms by which an influenza infection may trigger a stroke, including platelet activation and aggregation, inflammation or dehydration linked to thrombosis, impaired endothelial function, arterial dissection, and infection-induced cardiac arrhythmias. People immunized with the influenza vaccine are at lower risk of influenza infection and, as a result, are at a lower risk of experiencing a stroke through the mechanisms described above. Moreover, it is important to consider that individuals that get vaccinated are more likely to adopt other positive health-seeking behaviours and lifestyles which may contribute to the reduced risk of stroke compared to their non-immunized counterparts.

According to GlobalData epidemiologists, across the 16MM (US, UK, France, Germany, Spain, Italy, Japan, Australia, Brazil, Canada, China, India, Mexico, Russia, South Korea, and South Africa), diagnosed incident cases of acute ischemic stroke are expected to grow from 5.1 million cases in 2022 to 5.72 million cases by 2027, at a growth rate of 3% per year. Given the rapidly growing elderly population worldwide, GlobalData epidemiologists expect the incidence of stroke to increase over the coming years. While these study results are concerning, further research is needed to better understand and quantify the potential role of influenza vaccination as a public health strategy to prevent stroke.