Researchers found that getting COVID-19 and flu shots together — or just getting the high-dose or adjuvanted flu shot alone — can slightly raise the risk for strokes, according to government health officials. The association is more profound when the shots are given at the same time, and in those aged 85 and older.

A team at the US Food and Drug Administration (FDA) evaluated data from Medicare claims to come up with the conclusion.

In January, the FDA and the US Centers for Disease Control announced that their safety monitoring study — the Vaccine Safety Datalink — detected a small and uncertain stroke risk in older adults who got a Pfizer COVID-19 shot and a flu shot in the same day.

The FDA said the risk is small, and is about three strokes or transient ischemic attacks per every 100,000 doses given. The mechanism behind the increased risk may be the high-dose or adjuvanted flu vaccines, because they’re made to trigger the immune system so it responds better to the shot.

There’s also a slightly higher risk of stroke in people 65 and up who receive a high-dose flu vaccine, Medicare claims data revealed. That equates to about one or two strokes for every 100,000 flu shots. 

“The absolute risk is miniscule,” Steve Nissen, MD, a cardiologist and researcher at the Cleveland Clinic in Ohio, said. “I mean it is trivial in comparison to the risk for people over 85 of dying from COVID.”

Other research hasn’t found a higher risk for stroke after receiving a COVID-19 shot, flu shot, or both.

“Available data do not provide clear and consistent evidence of a safety problem for ischemic stroke with bivalent mRNA Covid-19 vaccines when given alone or given simultaneously with influenza vaccines,” said Tom Shimabukuro, MD, director of the CDC’s Immunization Safety Office. 

People should still get vaccinated, researchers say. William Schaffner, MD, an infectious disease expert at Vanderbilt University, said spreading out vaccines is the “reasonable thing to do.”

In September, experts said that getting the vaccines at the same time was safe and effective.