The U.S. Centers for Disease Control and Prevention (CDC) and Food and Drug Administration (FDA) said last week that they are investigating a possible link between Pfizer/BioNTech’s bivalent messenger RNA (mRNA) Comirnaty COVID biologic and an increased risk of a type of ischemic stroke among people 65 years of age and older. Data from the CDC’s Vaccine Safety Datalink (VSD) uncovered a “safety signal” suggesting that those in this age range are more likely to suffer an ischemic stroke 21 days after getting the bivalent Comirnaty than they are 22-44 days post-vaccination.1 2 3 4 5 6 7 8
According to the CDC:
Following the availability and use of the updated (bivalent) COVID-19 vaccines, CDC’s Vaccine Safety Datalink (VSD), a near real-time surveillance system, met the statistical criteria to prompt additional investigation into whether there was a safety concern for ischemic stroke in people ages 65 and older who received the Pfizer-BioNTech COVID-19 Vaccine, Bivalent. 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 22-42 following vaccination.8
CDC and FDA Launch Investigation
A spokesperson for the CDC said that the safety signal was first detected in late-November 2022. A CNBC article noted that the CDC “concluded the concern was persisting and launched an investigation.” The findings of the investigation are scheduled to be discussed at a meeting of the FDA’s Vaccines and Related Biological Products Advisory Committee on Jan. 26.3 4
An ischemic stroke is a type of stroke that originates in the brain. It occurs when there is a blockage in arteries that carry blood to the brain, depriving brain tissue of oxygen and nutrients and causing brain cells to die. Symptoms of stroke include trouble speaking and understanding what others are saying; paralysis or numbness of the face, arm or leg; problems seeing in one or both eyes; headache and trouble walking.9
“These strokes are not a confirmed adverse event at the moment,” said William Schaffner, MD of Vanderbilt University School of Medicine and the CDC’s Advisory Committee on Immunization Practices’ COVID-19 Vaccine Work Group. “It’s like a radar system. You’re getting a blip on the radar, and you have to do further investigation to discover whether that airplane is friend or foe.”3
An article in Politico quoted U.S. Representative Cathy McMorris Rodgers of Washington as saying, “These agencies must rapidly investigate, in an open and transparent manner, whether or not the vaccine may have contributed to the reported strokes.”5 Rep. McMorris Rogers added:
If there’s one lesson that the CDC and FDA should have taken away from the pandemic, it’s the importance of providing honest, clear, precise, and timely information to the American people about the potential risks and benefits of COVID-19 interventions, including vaccination.5
Other COVID Shots Linked to Blood Clotting
Blood clotting problems that can lead to strokes have been associated with other COVID shots, notably AstraZeneca/Oxford University’s Vaxzevria and Johnson & Johnson/Janssen’s Ad26.COV2.S adenovirus vectored vaccines. In early-2001, both vaccines were temporarily suspended in Europe and the United States due to numerous reports of a blood clotting disorder associated with the products. The FDA and European Medicines Agency (EMA) subsequently recommended updating the warning labels for the vaccines to advise the public of the potential risk of blood clotting.10 11 12 13
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1 Block J. Pfizer COVID-19 shot safety signal in seniors under investigation by CDC, FDA. Seeking Alpha Jan. 13, 2023.
2 Choi J. CDC and FDA find no increased risk of ischemic stroke for elderly who get Pfizer’s bivalent booster. The Hill Jan. 13, 2023.
3 Goodman B. CDC identifies possible safety issue with Pfizer’s updated Covid-19 vaccine but says people should still get boosted. CNN Jan. 13, 2023.
4 Kimball S. CDC says it’s ‘very unlikely’ Pfizer booster carries stroke risk for seniors after launching review. CNBC Jan. 13, 2023.
5 Leonard B, Gardner L. CDC, FDA see possible link between Pfizer’s bivalent shot and strokes. Politico Jan. 13, 2023.
6 Reuters. U.S. FDA, CDC see early signal of Pfizer bivalent COVID shot’s link to stroke. Jan. 13, 2023.
7 Sabes A. CDC identifies possible ‘safety concern’ for certain people receiving COVID vaccines. Fox News Jan. 13, 2023.
8 U.S. Centers for Disease Control and Prevention. CDC & FDA Identify Preliminary COVID-19 Vaccine Safety Signal for Persons Aged 65 Years and Older. Jan. 13, 2023.
9 Mayo Clinic. Stroke.
10 Cinone D. The FDA Just Added This Warning for the Johnson & Johnson Vaccine. BestLife Apr. 24, 2021.
11 Hendler C. After Blood Clot Reports, Some Countries Stop Using the Oxford/AstraZeneca COVID-19 Vaccine. The Vaccine Reaction Apr. 5, 2021.
12 Hobley N. Worry About Johnson & Johnson COVID Vaccine Safety Persists. The Vaccine Reaction Aug. 2, 2021.
13 Kansteiner F. AstraZeneca COVID-19 shot tagged with new warning in EU, highlighting rare blood clot risk. Fierce Pharma Apr. 7, 2021.