U.S. says Pfizer's bivalent COVID shot may be linked to stroke in older adults

U.S. drugmaker Pfizer Inc and German partner BioNTech's updated COVID-19 shot could be linked to a type of brain stroke in older adults, according to preliminary data analyzed by U.S. health authorities.

Citing one of many vaccine safety databases of the U.S. Centers for Disease Control and Prevention (CDC), health officials said on Friday that people 65 and older were more likely to have an ischemic stroke 21 days after receiving the Pfizer/BioNTech bivalent shot, compared with days 22-44.

An ischemic stroke, also known as brain ischemia, is caused by blockages in arteries that carry blood to the brain.

The safety concern requires more investigation and "it is very unlikely that it represents a true clinical risk", the authorities said.

Pfizer and BioNTech said in a statement that they have been made aware of limited reports of ischemic strokes in people 65 and older following vaccination with their updated shot.

"Neither Pfizer and BioNTech nor the CDC or the U.S. Food and Drug Administration (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," Pfizer added.

This safety concern has not been identified with Moderna's bivalent shot and both the CDC and FDA continue to recommend that everyone aged 6 months and older stay up-to-date with their COVID-19 vaccination.

Pfizer/BioNtech and Moderna's bivalent shots, which target both the original coronavirus and Omicron sub-variants, have been authorized for use in children 6 months and older.