CDC identifies possible safety issue with Pfizer’s updated Covid-19 vaccine, but says people should still be boosted


The US Centers for Disease Control and Prevention said on Friday there was a possible safety issue with the bivalent Covid-19 vaccine made by Pfizer and BioNTech but is unlikely to pose a real risk. . The agency said it continues to recommend people keep up to date with Covid-19 vaccines.

The CDC said one of its vaccine safety monitoring systems — a “near real-time monitoring system” called Vaccine Safety Datalink — detected a possible increase in a certain type of stroke in people age 65 and older who have recently received one of Pfizer’s updated reminders.

A rapid response analysis of this signal revealed that older adults who received a bivalent booster may be more likely to have ischemic strokes in the first three weeks after their injections, compared to weeks four through six.

Ischemic strokes, the most common form, are blockages of blood to the brain. They are usually caused by clots.

The Vaccine Safety Datalink, or VSD, is a network of major health systems across the country that provides data on vaccine safety and effectiveness via patient electronic health records. The CDC said it has identified possible confounding factors in the data from the VSD that may skew the data and require further investigation.

Of approximately 550,000 seniors who received Pfizer bivalent boosters and were followed by the VSD, 130 had strokes within three weeks of the shot, according to a CDC official who spoke to CNN under cover of anonymity as they were not authorized to share the data. . None of the 130 people died.

The number of strokes detected is relatively low, said Dr. William Schaffner, an infectious disease expert at Vanderbilt University and a member of the CDC Advisory Committee on Immunization Practices’ Covid-19 vaccine task force.

“These strokes are not a confirmed adverse event at this time,” he said. “It’s like a radar system. You get 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 was not detected with the Moderna bivalent booster, the CDC said in its advisory.

The agency noted that it had searched and failed to find the same increase in strokes in other large collections of medical records, including those maintained by Medicare, the U.S. Department of Veterans Affairs, as well. as its vaccine adverse event reporting system, known as VAERS.

Neither Pfizer nor other countries that use the vaccine have seen an increase in this type of stroke, the agency said, and the signal has not been detected in any other databases.

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 possible safety concerns with the vaccine.

“Although the totality of the data currently suggests that the signal in the VSD is very 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 guards monitoring systems detects a signal,” the notice reads.

“The 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 Jan. 26 meeting of the Vaccines and Drugs Advisory Committee. FDA Related Biologics.”

Pfizer said in a statement Friday, “Neither Pfizer and BioNTech nor the CDC or the U.S. Food and Drug Administration (FDA) have observed similar results in many other monitoring systems in the U.S. and around the world. world and there is no evidence to conclude that ischemic stroke is associated with the use of companies’ COVID-19 vaccines.

“Compared to published incidence rates of ischemic stroke in this elderly population, the companies have observed a lower number of ischemic strokes reported after vaccination with the adapted bivalent Omicron BA.4/BA.5 vaccine to date. ”

Bivalent boosters from Pfizer/BioNTech and Moderna protect against the original strain of coronavirus as well as the Omicron BA.4 and BA.5 subvariants. According to CDC data, only about 50 million Americans ages 5 and older have had it since they were cleared last fall.

Schaffner said he was part of a Thursday briefing with members of the Covid-19 vaccine task force. He could not share specific details of the briefing, but said the safety signal was discussed.

His biggest takeaway was that the security monitoring system is working.

It is very likely to be a false signal, he said, but it is being investigated, which is important.

“You want a monitoring system that occasionally sends false signals. If you don’t get any signals, you’re worried about missing things.”

Schaffner said he would absolutely tell people to get their Covid-19 booster if they haven’t already – even those 65 and over.

“There is no doubt that the risk of a whole range of adverse events, including hospitalization, is much, much greater with Covid-19 than with the vaccine,” he said.

He also said the signal – if real – could be more of a numbers factor than an indication that one manufacturer’s vaccine is riskier than the other.

Nearly two-thirds of people in the United States who received an updated booster — 32 million — received Pfizer, compared to about 18 million Moderna vaccines.


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