FDA reports initial 'no signal' for stroke risk with Pfizer boosters, launches concomitant flu shot study

2023-01-26

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The FDA hasn’t detected any potential safety signals, including for stroke, in people aged 65 years and older who have received Pfizer’s bivalent Covid booster, one senior official told members of the agency’s Vaccines and Related Biological Products Advisory Committee (VRBPAC) on Thursday. The update comes as the FDA and CDC investigate a “preliminary signal” that may indicate an increased risk of ischemic stroke in older Americans who received Pfizer’s updated shot. As of Jan. 11, 21.3 million bivalent boosters had been administered in those 65 years and older, according to Tom Shimabukuro, director of the CDC’s Immunization Safety Office. Just one of the CDC’s multiple safety systems, Vaccine Safety Datalink, found a potential problem, according to a joint statement from the FDA and CDC: While Nicola Klein, director of the Kaiser Permanente Vaccine Study Center, said that monitoring system has been “signaling for several weeks,” she also noted that “results may have been influenced by confounders that vary over time.” Researchers saw a “subtle although present” cluster of patients 65 and older who experienced ischemic stroke 11 to 22 days after receiving the booster, while the number of incidents appeared to reduce over time. She also added that there may have been lower-than-expected incidence rates in the comparator group. Last week, Israel and EU drug regulators announced they had not found a link between the booster shot and ischemic stroke. “There have been no excess reports of stroke from VAERS. I just reported on what we found in our CMS sequential analysis showing no increased risk in stroke. The Veterans Affairs database has also done a preliminary run and did not find an increase in stroke,” said Richard Forshee, deputy director of the FDA’s Office of Biostatistics and Pharmacovigilance. He confirmed on Thursday that the only safety signal observed in the adult population following the Pfizer booster has been myocarditis and pericarditis in individuals between 18 and 35 years old, which was also observed following the monovalent primary vaccine series. And while the CDC’s analyses suggest a potential heightened risk among those who received a concomitant flu vaccine, Forshee said the FDA’s analysis — including 4.25 million doses of Pfizer’s vaccine in those 65 and older, 38% of whom received a concomitant flu shot — hasn’t detected such a risk. “We’re continuing to do more work to segment out the different influenza vaccines administered. And again no signal at this time has been seen for hemorrhagic stroke even though we have 38% that received a concomitant influenza vaccination,” Forshee said. Forshee said the agency has launched a formal epidemiological study focusing in particular on concomitant administration of a high-dose or flu vaccine.

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