Fact check: Post falsely claims that FDA said Pfizer vaccines cause blood clots

Sudiksha Kochi, USA TODAY
·5 min read
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The claim: The FDA said Pfizer vaccines cause blood clotting

The Food and Drug Administration limited the use of the Johnson & Johnson vaccine in early May due to the risk of thrombosis with thrombocytopenia syndrome, a condition that causes blood clots to form.

Some social media users are falsely claiming the agency recently announced the Pfizer vaccine carries a blood clot risk, too.

"So the FDA finally came out and said that Pfizer’s Covid shot causes blood clots?" reads a Dec. 17 tweet (direct link, archived link) from the Hodgetwins, a conservative political commentator duo. "Only 2 years late!"

Elon Musk tweeted in reply, "Much will come to light as Fauci loses power."

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The Twitter exchange generated more than 300,000 likes in less than a week. It was also shared on Instagram on Dec. 17 (direct link, archived link), where it generated more than 140,000 likes in a week.

But the claim is baseless.

The assertion stems from a recently published study led by FDA researchers and other medical professionals that found a "statistical signal" between pulmonary embolism – blood clots in the lungs – and the Pfizer vaccine. But this signal does not prove the Pfizer vaccine causes blood clots, medical experts told USA TODAY.

USA TODAY reached out to the Hodgetwins and the social media user who shared the claim for comment. Musk did not reply to USA TODAY's request for comment after being contacted on Twitter and through Twitter and Tesla's press offices.

Pfizer vaccine doesn't cause blood clotting, experts say

The Pfizer vaccine doesn't cause blood clots, and the Dec. 1 study does not prove otherwise, according to Dr. Yazan Abou-Ismail, a hematologist at the University of Utah.

The study monitored 14 adverse events following COVID-19 vaccinations given to over 30 million people age 65 and older from Dec. 11, 2020, through Jan. 15, 2022. It uses data from the Centers for Medicare & Medicaid Services. Researchers then compared the frequency of each event to the expected rate prior to COVID-19 vaccination.

They detected a "statistical signal" between pulmonary embolism and the Pfizer vaccine. But this signal merely shows an association with the vaccine, not any sort of causation, William Petri, a professor of internal medicine and pathology at the University of Virginia, told USA TODAY in an email.

FDA spokesperson Abigail Capobianco also told USA TODAY in an email that the agency has not found any new causal relationships between the Pfizer vaccine and potential "adverse events of special interest" identified in 2021. Pulmonary embolism is one of those events.

"The association that (the statistical signals) show may have nothing to do with vaccination," Petri said. It "may be due to the people receiving vaccines already being at higher risk for blood clots to the lung due to their older age, comorbidities or nursing home residence."

Fact check: False claim that FDA said vaccines are linked to heart attacks, deaths

Abou-Ismail agreed, noting that the study did not account for underlying risk factors.

Other limitations of the study include early warning systems falsely identifying a signal or diagnosis billing codes in claims data underestimating or overestimating certain medical conditions, the authors said.

"Because an early warning system does not prove that the vaccines cause these outcomes, more robust epidemiologic studies ... are underway to further evaluate these signals," the authors wrote in the study.

Dr. Richard Martinello, an infectious disease specialist at Yale University, expressed a similar sentiment noting the signal the researchers found requires further study to determine if a true association exists.

The Associated Press, PolitiFact, AFP, Factcheck.org and Health Feedback also debunked the claim.

USA TODAY has debunked other claims related to the Pfizer vaccine, including baseless assertions that 80,000 pages of Pfizer data show the vaccine has a 12% efficacy rate and harms fetuses, and that a Pfizer trial reported 42,000 adverse events and 1,200 fatalities.

Our rating: False

Based on our research, we rate FALSE the claim that the FDA said Pfizer vaccines cause blood clotting. The claim stems from a Dec. 1 study led by FDA researchers that found a "statistical signal" between pulmonary embolism and the Pfizer vaccine. But this signal does not prove the Pfizer vaccine causes blood clots, a conclusion that would require further study, medical experts told USA TODAY.

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This article originally appeared on USA TODAY: Fact check: No link between Pfizer vaccines, blood clots