U.S. surveillance system flags possible safety signal for Pfizer’s bivalent vaccine and stroke risk

The U.S. Centers for Disease Control and Prevention (CDC) and the U.S. Food and Drug Administration (FDA) have announced that one of their surveillance systems—the Vaccine Safety Datalink—has flagged a possible preliminary COVID-19 vaccine safety signal between the use of the Pfizer-BioNTech bivalent COVID-19 vaccine and the development of ischemic strokes in people 65 years of age or older.1-3 It is important to tell patients that this is just a potential safety signal flagged by one U.S. surveillance system and the CDC and FDA are further investigating. No increased risk of ischemic stroke was seen in a large study of bivalent vaccines (from Pfizer-BioNTech and Moderna) using the U.S. Centers for Medicare and Medicaid Services database; a preliminary study using the U.S. Veterans Affairs database; the Vaccine Adverse Event Reporting System (VAERS) managed by the CDC and the FDA; or in Pfizer-BioNTech’s global safety database.2 No increased risk has been flagged with the Moderna bivalent COVID-19 vaccine.2 Patients should also be reassured that this possible link has not been observed in Canada or by other international regulatory agencies. The CDC and FDA indicate that the totality of data currently suggests that it is very unlikely that the signal in the Vaccine Safety Datalink represents a true clinical risk. Therefore, the CDC is not recommending any changes to vaccination practices; everyone six months of age and older should continue to stay up-to-date with COVID-19 vaccinations.1,2 In Canada, evidence indicates that the benefits of COVID-19 vaccines continue to outweigh the risks. As of Jan. 1, 2023, more than seven million doses of mRNA bivalent vaccines have been administered in Canada. To date, the Public Health Agency of Canada (PHAC) and Health Canada have not observed any elevated risk or any signals for thromboembolic events or vascular events following administration of these vaccines.1,3 To date, fewer than five reports of ischemic stroke have been submitted to the PHAC and Health Canada following receipt of an mRNA bivalent vaccine; only one of these followed the Pfizer-BioNTech bivalent vaccine and was for an individual aged 65 years or older.1 Overall, in Canada, available data show that there is no indication of a signal related to ischemic stroke and mRNA bivalent vaccines. Health Canada and the PHAC will continue to monitor the safety of COVID-19 vaccines approved in Canada to ensure that their benefits continue to outweigh their risks.1,3 References 1. US CDC and FDA Surveillance System Flags Possible Safety Signal Between Pfizer’s Bivalent Vaccine and Ischemic Strokes. Health Canada has not observed an elevated risk or any signals. Toronto Public Health Physician’s e-Newsletter; January 27, 2023. (accessed January 30, 2023). 2. Centers for Disease Control and Prevention. CDC & FDA identify preliminary COVID-19 vaccine safety signal for persons aged 65 years and older. Updated January 13, 2023. 3. Government of Canada. Reported side effects following COVID-19 vaccination in Canada. Last updated on January 20, 2023. (accessed January 30, 2023).

U.S. surveillance system flags possible safety signal for Pfizer’s bivalent vaccine and stroke risk

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