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(CNN) --
The US Centers for Disease Control and Prevention (CDC) said Friday that there is a potential safety issue with the bivalent covid-19 vaccine made by Pfizer and BioNTech, but which is unlikely to pose any real risk.
The agency said it continues to advise people to stay up-to-date with their Covid-19 vaccinations.
The CDC said that one of its vaccine safety monitoring systems, a "near real-time surveillance system" called the Vaccine Safety Datalink (VSD), detected a possible increase in a certain type of stroke in people older than 65. years old who had recently received one of Pfizer's updated booster shots.
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A rapid-response analysis of that signal revealed that older people who received a bivalent booster might be more prone to these types of strokes in the first three weeks after their vaccinations, compared with weeks four to six.
According to the CDC, the same safety signal has not been detected with Moderna's bivalent booster.
However, the CDC notes that they have searched and have not found the same increase in strokes in other large collections of medical records, including those maintained by Medicare, the US Department of Veterans Affairs, as well as its System of Medical Records. Notification of Vaccine Adverse Effects, known as VAERS.
Neither Pfizer nor other countries using the vaccine have seen an increase in such strokes, according to the agency, and the signal was not detected in any other databases.
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The CDC says it is not recommending any changes to vaccination practices at this time and that the risks posed by Covid-19 to older adults continue to outweigh any potential safety concerns with the vaccine.
"While the totality of the data currently suggests that the VSD signal is highly unlikely to represent a true clinical risk, we believe it is important to share this information with the public, as we have done in the past, when one of our security monitoring detects a signal," the notice says.
"CDC and FDA will continue to evaluate additional data from these and other vaccine safety systems. These additional data and analyzes will be discussed at the upcoming January 26 meeting of the FDA's Advisory Committee on Vaccines and Related Biologicals."
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