In the peer-reviewed observational study, published on Wednesday in Neurology, the medical journal of the American Academy of Neurology, researchers collected data from a health care database in Spain called BIFAP (Base de datos para la Investigación Farmacoepidemiológica en el Ámbito Público) and identified people who were 40-years-old or older and had the first stroke over a 14-year period.
The researchers compared each person who had a stroke to five people of the same age and sex who didn't.
Next, the researchers examined whether patients had been administered the flu vaccine at least 14 days prior to their stroke or before then.
What did the researchers find?
The researchers found that those in the study who were vaccinated were older, had medical checkups with their physicians more often over the last year, were more likely to be on medication and had higher incidences of vascular diseases and other risk factors than the unvaccinated participants.
And yet, the vaccinated participants had a lower risk of stroke than their unvaccinated counterparts.
“Compared with unvaccinated, vaccinated subjects were older, had more visits to their PCP (personal care provider) in the last year before the index date and presented a higher prevalence of vascular disease and risk factors, as well as higher use of co-medication. Such differences between vaccinated and unvaccinated subjects were even more pronounced in people aged 65-years-old,” the researchers said.
The researchers assessed the statistical connection between flu vaccination and ischemic stroke using conditional logistic regression models.
After adjusting for traits such as age or chronic health conditions such as high blood pressure and high cholesterol that increase the risk of stroke, the researchers found that patients who had gotten a flu shot were 12% less likely to have a stroke than those who had not gotten a flu shot.
What about the pneumonia vaccine?
The researchers also studied whether the pneumonia vaccine had any impact on the risk of stroke, but they found it had no effect.
“These results provide yet another reason for people to get their yearly flu shot, especially if they are at an increased risk of stroke. To be able to reduce your risk of stroke by taking such a simple action is very compelling.”Francisco J. de Abajo, MD, MPH, PhD, University of Alcalá, Madrid, Spain
Study author Dr. Francisco J. de Abajo from the University of Alcalá in Madrid, Spain, said that the findings provide “yet another reason for people to get their yearly flu shot, especially if they are at an increased risk of stroke. To be able to reduce your risk of stroke by taking such a simple action is very compelling.”
As the study was observational, it does not prove that getting the flu shot reduces the risk of stroke but rather suggests a correlation. Other factors that were not accounted for may impact the risk of stroke.