Following an analysis of vaccine surveillance data, the Centers for Disease Control and Prevention (CDC) and the Food and Drug Administration (FDA) say they have found no evidence of increased risk of ischemic stroke among people 65 and older who receive Pfizer’s bivalent booster.
After Pfizer’s updated, bivalent COVID-19 booster dose was made available, the CDC said its Vaccine Safety Datalink prompted additional investigation into concerns over whether the shot presented a safety concern for people 65 and older.
An ischemic stroke, more common than hemorrhagic strokes, occurs when a blood clot blocks a blood vessel in the brain, stopping blood flow and potentially leading to brain cells dying. If a stroke is not treated quickly, the effects can be debilitating.
A similar safety signal was not identified for Moderna’s bivalent booster dose.
“Rapid-response investigation of the signal in the VSD raised a question of whether people 65 and older who have received the Pfizer-BioNTech COVID-19 Vaccine, Bivalent were more likely to have an ischemic stroke in the 21 days following vaccination compared with days 22-44 following vaccination,” the CDC said.
Studies conducted with the use of databases from the Centers for Medicare and Medicaid Services and Veterans Affairs did not indicate or show an increased risk for ischemic stroke, according to the CDC. The Vaccine Adverse Event Reporting System managed by both the CDC and FDA also did not show an increase in reports of ischemic stroke following a bivalent booster dose.
The CDC concluded that no change was needed for its recommendation regarding the bivalent boosters, which advises that everyone over the age of 6 months stays up to date on their COVID-19 vaccinations.
When COVID-19 vaccines became available, concerns were raised over the possible rare side effects following administration. Several European countries in 2021 ceased administering the COVID-19 vaccine developed by AstraZeneca — not an mRNA vaccine like Pfizer’s — over concerns the shot had caused some recipients to develop blood clots.
While the possible association between COVID-19 vaccines and strokes is not entirely clear, researchers and physicians have repeatedly stressed that the risk of stroke due to COVID-19 infection is higher than the risk caused by immunization.