The US Centers for Disease Control and Prevention (CDC) and the Food and Drug Administration (FDA) said on Friday that a CDC vaccine database had uncovered a possible safety issue in which 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.

The FDA and CDC said that other large studies, the CDC's Vaccine Adverse Event Reporting System, other countries' databases and Pfizer-BioNTech's databases had not flagged this safety issue, adding that it requires more investigation.

Pfizer and BioNTech said in a statement, "Neither Pfizer and BioNTech nor the CDC or FDA have observed similar findings across numerous other monitoring systems in the US and globally and there is no evidence to conclude that ischemic stroke is associated with the use of the companies' COVID-19 vaccines.”