Elderly people may have an increased risk of stroke caused by blood clots in the brains if they receive both the COVID booster and a flu shot in the same visit, a new study suggests.
Older adults who received both shots in the same visit last year had a 20-35% increased stroke risk, according to the study, which was funded by the Food and Drug Administration (FDA).
The results showed about three strokes for every 100,000 doses given.
The study suggested the increased stroke risk may be primarily driven by the flu shots rather than the COVID vaccines. Nevertheless, the results have sparked concerns.
The study examined the Medicare claims of more than 5.3 million adults age 65 and older who received a bivalent Pfizer or Moderna COVID vaccine.
Those age 65 or older who got a bivalent vaccine and a high-dose flu shot at the same time had an increased risk of blood clots in their brains. The high-dose flu shot is only approved for people 65 and older.
Those 85 and older who got the Pfizer vaccine also had a higher risk of stroke caused by blood clots even without taking the flu shot at the same time, the study found.
The study also found a very slight increase in stroke risk for those 65 and older who had only gotten a high-dose flu shot, about one to two strokes per 100,000 doses.
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The study is not yet peer-reviewed and is observational, meaning it can only show associations, not prove cause and effect. Some experts cautioned that the results are preliminary and could have another explanation such as elderly people being at higher risk for stroke already because of their age.
The study was triggered by a January public communication from the Centers for Disease Control (CDC) and FDA stating that one of their vaccine safety monitoring studies had suggested a small risk of stroke for older adults who received a Pfizer COVID shot and a high-dose flu shot on the same day.
“The review conducted in this preprint paper is part of our ongoing safety surveillance efforts, which utilize a variety of data sources,” the Food and Drug Administration told ABC, adding that the agency remains confident in the COVID vaccine.
Pfizer recently released a commercial promoting getting the COVID vaccine and the flu shot at the same time, or “two things at once.”
The ad spot features Travis Kelce, a tight end for the Kansas City Chiefs, who shows the camera two Band-Aids on his arm for the two shots.
“Travis, did you know you can get this season’s COVID-19 shot when you get your flu shot?” a woman asks the NFL player in the ad.
“Huh, two things at once,” Kelce responds. The ad then shows Kelce performing a series of two activities at once such as grilling while mowing the lawn and riding a hot air balloon while speaking on the radio.
The Kansas City Chiefs did not immediately respond to a request for comment.