Rapid Review Quiz: Unusual Vaccine News

Michael Stuart Bronze, MD


February 13, 2023

According to a large population-based study, influenza vaccination was associated with a reduced risk for stroke among adults, even those who are not at high risk. Specifically, in the 6 months after a flu shot, the risk for stroke among patients who received vaccination was about 23% lower, regardless of sex, age, or underlying health conditions.

Researchers analyzed administrative data from all residents of Alberta from September 2009 to December 2018 using the province-wide Alberta Health Care Insurance Plan. The plan provides free seasonal influenza vaccines to residents. The team looked for stroke events, including subarachnoid hemorrhage, acute ischemic stroke, intracerebral hemorrhage, and transient ischemic attack. Accounting for multiple demographic factors and factors related to stroke risk (sex, age, income, location, atrial fibrillation, anticoagulant use, diabetes, chronic obstructive pulmonary disease, and hypertension) the team analyzed the risk for stroke events in the previous 6 months among those with or without a flu shot.

Among 4.1 million adults, about 1.8 million (43%) received at least one vaccination during the study. Almost 97,000 people received a flu vaccine every year they were in the study, including almost 30,000 who received a flu shot for each of the 10 flu seasons observed.

Although crude incidence of stroke was higher among people who received an influenza vaccination (1.25%) vs no flu vaccination (0.52%), after adjusting for the various factors discussed above, flu vaccination within the previous 6 months was associated with a 23% reduced risk for stroke.

Vaccination was associated with a greater relative reduction in stroke risk in lower income groups, younger age groups, and those with chronic obstructive pulmonary disease, diabetes, and anticoagulant use.

Among 2.4 million people observed for the entire study period, vaccination protection increased with the number of vaccines received. People who were vaccinated each year had a significantly lower risk for stroke than did those who received one shot.

Learn more about influenza.


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