On Friday, the Centers for Disease Control and Prevention (CDC) and the Food and Drug Administration (FDA) issued a joint statement that a potential link between Pfizer-BioNTech’s bivalent Covid-19 vaccine and ischemic strokes in people over the age of 65 has been detected by the CDC's Vaccine Safety Datalink surveillance system. The data suggests a possible increased risk of ischemic strokes 21 days after receiving the shot, compared to 22-44 days after. The agencies, however, are not recommending any changes to vaccine distribution at this time, as no other safety signals have been detected and studies of data from the Centers for Medicare and Medicaid Services, Veterans Affairs, the Vaccine Adverse Event Reporting System and Pfizer-BioNTech have not yielded similar results. Additionally, no such signal has been detected with Moderna’s bivalent vaccine.
The CDC stated that it is “very unlikely” this signal represents “a true clinical risk,” and that they and the FDA will continue to evaluate data regarding this issue. The bivalent shots, known as "updated boosters," have been available to those 12-years-old and older since September, and to those ages 5 to 11 and some children between the ages six months and four years old in October and December, respectively. A CDC study released in December found that the bivalent doses were 56% more effective in preventing Covid compared to no vaccine.
It is important to note that the agencies are not recommending any changes to vaccine distribution, and that the data suggests it’s “very unlikely” that this signal represents “a true clinical risk.” Nevertheless, the CDC and FDA will continue to evaluate data regarding this issue.