The United States Centers for Disease Control and Prevention (CDC) and the country's Food and Drug Administration (FDA) said on Friday they will launch an additional investigation to determine if the updated bivalent Pfizer/BioNTech COVID-19 vaccine could increase the risk of an ischemic stroke in people over the age of 65.

"Rapid-response investigation of the signal in the VSD [Vaccine Safety Datalink] 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 agencies stressed. "Although the totality of the data currently suggests that it is very unlikely that the signal in VSD represents a true clinical risk, we believe it is important to share this information with the public," they added.

The CDC and the FDA pointed out that there have been no preliminary safety signals with the Moderna COVID-19 jab.