The US Food and Drug Administration (FDA) and US Centers for Disease Control and Prevention (CDC) are investigating whether Pfizer/BioNTech’s updated COVID-19 vaccine could be linked with an increased risk of ischaemic stroke in older adults.
The investigation was prompted by preliminary data from the CDC’s vaccine safety monitoring system, which raised a question of whether people aged 65 years and older who received the bivalent vaccine were more likely to have an ischaemic stroke in the 21 days following vaccination, compared with days 22-42.
An ischaemic stroke, also known as brain ischaemia, occurs when the blood supply to part of the brain is interrupted or reduced, preventing brain tissue from receiving oxygen and nutrients.
No other safety systems and multiple subsequent analyses to date have flagged a similar safety concern with the vaccine, the FDA and CDC said.
This includes analysis of other large vaccine data sets from Medicare, the US Department of Veterans Affairs, Pfizer/BioNTech’s own monitoring programmes and the Vaccine Adverse Event Reporting System, which is managed by the CDC and FDA.
“Although the totality of the data currently suggests that it is very unlikely that the signal in [Vaccine Safety Datalink] represents a true clinical risk, we believe it is important to share this information with the public, as we have in the past, when one of our safety monitoring systems detects a signal,” the health authorities said in a statement.
They added that they will continue to evaluate additional data from vaccine safety systems, with the additional findings set to be discussed at the upcoming meeting of the FDA’s Vaccines and Related Biological Products Advisory Committee on 26 January.
Pfizer and BioNTech said in a statement that they have been made aware of the report.
“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 ischaemic stroke is associated with the use of the companies’ COVID-19 vaccines,” the companies said.
The CDC said it will not be making any changes to its vaccine recommendations at this time and will continue to recommend that everyone aged six months and older stay up-to-date with their COVID-19 vaccinations.