The US Centers for Disease Control and Prevention said Friday that there is a potential safety issue with the bivalent Covid-19 vaccine made by Pfizer and BioNTech, but that it is unlikely to pose any real risk. The agency said it continues to recommend that people stay up to date with their covid-19 vaccinations.
The CDC said one of its vaccine safety monitoring systems, a “near real-time surveillance system” called the Vaccine Safety Data Link, detected a possible increase in a certain type of stroke in people 65 and older. more than recently received one of Pfizer’s updated booster shots. .
A rapid response analysis of that signal revealed that older people who received a bivalent booster might be more likely to have ischemic strokes within the first three weeks after their injections, compared with weeks four to six.
Ischemic strokes, the most common form, are blockages of blood to the brain. They are usually caused by clots.
The Vaccine Safety Data Link, or VSD, is a network of large health systems across the country that provides data on the safety and efficacy of vaccines through electronic health records of patients. The CDC said it had identified potential confounding factors in the data coming from the VSD that may be skewing the data and need further investigation.
Of approximately 550,000 older adults who received Pfizer bivalent boosters and were tracked by the VSD, 130 suffered strokes within three weeks of the injection, according to a CDC official who spoke to CNN on condition of anonymity because they were not authorized to share the data. . None of the 130 people died.
The number of detected strokes is relatively small, said Dr. William Schaffner, an infectious disease expert at Vanderbilt University and a member of the Covid-19 Vaccine Task Force of the CDC’s Advisory Committee on Immunization Practices.
“These strokes are not a confirmed adverse event at this time,” he said. “It’s like a radar system. You are receiving a signal on the radar and you have to investigate further to find out if that plane is friend or foe.”
The same safety signal has not been detected with the Moderna bivalent booster, the CDC said in its advisory.
The agency noted that it has searched and has not been able to find 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 Stroke Reporting System. vaccine adverse events, known as VAERS.
Neither Pfizer nor other countries using the vaccine have seen an increase in this type of stroke, the agency said, and the signal was not detected in any other database.
The CDC says it is not recommending any changes to vaccination practices at this time and that the risks of Covid-19 for older adults continue to outweigh any potential safety concerns with the vaccine.
“While the totality of the data currently suggests that the signal in VSD is highly unlikely to pose any real 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 custodians security monitoring systems detect 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.”
Pfizer said in a statement on Friday: “Neither Pfizer nor BioNTech nor the CDC nor the US Food and Drug Administration (FDA) have observed similar findings in many other monitoring systems in the US and in worldwide and there is no evidence to conclude that ischemic stroke is associated with the use of the company’s COVID-19 vaccines.
“Compared to published incidence rates of ischemic stroke in this older population, to date companies have observed fewer reported ischemic strokes after vaccination with the adapted bivalent Omicron BA.4/BA vaccine. .5″.
The Pfizer/BioNTech and Moderna bivalent boosters protect against the parent strain of the coronavirus, as well as the Omicron BA.4 and BA.5 subvariants. Only about 50 million Americans ages 5 and older have gotten them since they were approved last fall, according to CDC data.
Schaffner said he was part of a briefing Thursday with members of the Covid-19 Vaccine Task Force. She couldn’t share specific details about the briefing, but said the security signal was discussed.
His biggest conclusion was that the security surveillance system is working.
It’s very likely a false signal, he said, but it’s being investigated, which is important.
“You want a surveillance system that will occasionally send out false signals. If you’re not getting any signals, you’re worried you’re missing things.”
Schaffner said he would absolutely tell people to get their Covid-19 booster if they haven’t already, including those 65 and older.
“Without question, the risk of a whole host of adverse events, including hospitalization, is much, much higher with Covid-19 than with the vaccine,” he said.
He also said the signal, if real, may be more of a numbers factor than an indication that one manufacturer’s vaccine is riskier than another.
Nearly two-thirds of people in the US who got an upgraded booster (32 million) received Pfizer, compared to about 18 million Moderna shots.