A new study did not uncover evidence of heightened stroke risk among those 65 and up after they received COVID-19 shots. However, it did reveal a link in this population between flu shot and stroke, though authors said that there weren’t consistent increases in stroke risk after the high-dose or adjuvanted flu shots.
Researchers evaluated the risk related to the flu shot at several time periods: from 2016 to 2017, 2017 to 2018, and 2018 to 2019 during the flu season. Their report was published Monday in JAMA Network Open.
“Although we detected associations in the primary and age subgroup analyses, we did not observe consistent increased stroke risk following high-dose or adjuvanted influenza vaccination from 2016 to 2019,” the authors wrote.
Participants were placed into age subgroups: 65-74 years old, 75-84 years old and those over the age of 85. The participants were enrolled in Medicare, and none of them lived in a nursing home for at least one year before getting vaccinated for flu and COVID-19. The median age of participants was 74. The team looked at stroke risk through 42 days after vaccination as part of the risk window, and then from 43 to 90 days, which was considered the control window.
There were a total of 29,730 stroke cases in 2016 to 2017, 34,518 cases in 2017 to 2018 and 36,869 cases in 2018 to 2019. During the 2016 to 2017 time span, researchers noted a hemorrhagic stroke risk during the 22- to 42-day risk window, but no association was found in the other years or control window. In 2018 to 2019, the investigators noted an association in those 85 and older for nonhemorrhagic stroke and/or transient ischemic attack during the 1- to 21-day risk window.
The authors did acknowledge some limitations; specifically that they only evaluated vaccinated participants as part of their research.
“While influenza infection is a known trigger for stroke, we could not account for any protective effect of vaccination,” the authors wrote. “The clinical significance of any potential risk of stroke following vaccination must be carefully considered with known benefits of influenza vaccination.”
