who got the shot, the Centers for Disease Control and Prevention and the Food and Drug Administration said in a joint news release.
The release did not recommend people change their vaccine practices, saying the database finding probably did not represent a “true clinical risk.” The CDC said everybody, including people over 65, should stay up to date on their COVID vaccines, including the bivalent booster.
The news release said the Vaccine Safety Datalink (VSD), “a near real-time surveillance system,” raised a safety concern about the Pfizer/BioNTech booster.
“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 news release said.
Ischemic strokes are blockages of blood to the brain, often caused by blood clots.
“Although the totality of the data currently suggests that it is very unlikely that the signal in VSD (Vaccine Safety Datalink) represents a true clinical risk, we believe it is important to share this information with the public, as we have in the past, when one of our safety monitoring systems detects a signal,” the release said.
No higher likelihood of strokes linked to the Pfizer bivalent vaccine had been found by Pfizer/BioNTech, the Department of Veterans Affairs, the Vaccine Adverse Event Reporting System maintained by the CDC and the FDA, or other agencies that monitor reactions of vaccines, the news release said. No safety issues about strokes have been identified with the Moderna bivalent vaccine.
CNN, citing a CDC official, reported that about 550,000 seniors who got Pfizer bivalent boosters were tracked by the VSD, and 130 of them had strokes within 3 weeks of getting the shot. None of those 130 people died, CNN said. The official spoke on the condition of anonymity because they weren’t authorized to share the data.
The issue will be discussed at the January meeting of the FDA’s Vaccines and Related Biological Products Advisory Committee.
In a joint statement, Pfizer and BioNTech said: “Neither Pfizer and BioNTech nor the CDC or FDA have observed similar findings across numerous other monitoring systems in the U.S. and globally and there is no evidence to conclude that ischemic stroke is associated with the use of the companies’ COVID-19 vaccines.”
Bivalent boosters contain two strains of vaccine – one to protect against the original COVID-19 virus and another targeting Omicron subvariants.
A version of this article first appeared on WebMD.com.