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A study by the U.S. Food and Drug Administration found statistical signals for “modestly elevated risks” in four safety outcomes after Pfizer COVID-19 vaccination, including pulmonary embolism, in people ages 65 and older.
The study used data from the Centers for Medicare and Medicaid Services. Its authors noted several limitations of the analysis, including not adjusting for underlying factors, such as comorbidities.
The researchers said the findings do not show causation from the vaccines and the FDA is not taking regulatory action because more robust study is needed. They said the benefits of vaccination outweigh the risks of COVID-19 infection.
A recent study by the U.S. Food and Drug Administration about vaccine safety surveillance in elderly Americans is being used by some on social media to incorrectly claim that the agency announced that the Pfizer COVID-19 vaccine causes blood clots.
A Dec. 17 Instagram post by the Hodgetwins, a pair of conservative commentators, read, "So the FDA finally came out and said that Pfizer’s Covid shot causes blood clots? Only 2 years late!"
The post shared a screenshot of a tweet from the same user name that showed Twitter owner Elon Musk amplifying the claim to his 122 million followers with the reply, "Much will come to light as (Dr. Anthony) Fauci loses power."
The Instagram post was flagged as part of Facebook’s efforts to combat false news and misinformation on its News Feed. (Read more about our partnership with Meta, which owns Facebook and Instagram.)
But researchers did not say that the Pfizer vaccine caused blood clots. Their findings should be "interpreted cautiously," they concluded, "because the early warning system does not prove vaccines cause the safety outcomes."
The FDA has been monitoring the safety of the COVID-19 vaccines available in the U.S., and researchers released new findings from what they called a nationally representative early warning system on Dec.1.
The study, published in the journal "Vaccine," evaluated 14 safety outcomes following COVID-19 vaccination. It looked at data from the U.S. Centers for Medicare and Medicaid Services, covering more than 30 million people ages 65 and older — about 17 million of whom had been vaccinated — from Dec. 11, 2020, through Jan. 15, 2022.
Researchers said they compared the rate of observed safety outcomes with expected rates prior to COVID-19 vaccination. They found "modestly elevated risks" in four categories following vaccination with Pfizer’s vaccine.
The four areas that met the threshold for a statistical signal were:
pulmonary embolism (when a blood clot gets stuck in the lungs);
acute myocardial infarction (heart attack);
disseminated intravascular coagulation (an abnormal blood clotting condition);
and immune thrombocytopenia (a blood platelet disorder).
Researchers said no statistical signals were found in any categories after someone received the Moderna or Johnson & Johnson vaccines.
The findings varied when compared with different control groups. For example, when they compared the data with the "peri-COVID" period (Jan. 1, 2020 through Dec. 10, 2020, when COVID began and before vaccines were available), the statistical signal for pulmonary embolism was no longer there. But the signal remained when compared against people in an in-patient setting.
"To me the only take home from the study is that there was no strong association, if any, between the vaccines and any of the 14 adverse outcomes studied," said Dr. Yazan Abou-Ismail, a University of Utah assistant professor and thrombosis expert who specializes in diagnosing and treating blood clots. "The modest correlation that was found with four of those outcomes was not consistent with different types of analyses in the same study."
The report, which was an update of initial results the FDA disclosed in July 2021, said the statistical signals are "not necessarily causal" from vaccines and may be due to other factors.
"Database studies have major limitations, which is why they are not really a standard in evaluating safety or efficacy of anything," Abou-Ismail said.
We reached out to the FDA and one of the study’s authors but did not immediately get a response.
But in their findings, the researchers noted several limitations of their study, such as the analysis not adjusting for underlying risk factors such as comorbidities.
Smoking, for instance, is a known risk factor for clots, so if one group had more smokers, that could affect the results, Abou-Ismail said.
In addition, certain conditions may be under or overestimated due to diagnosis billing codes in claims data because of reimbursement priorities, the researchers wrote.
The researchers added that the report’s findings may not be "generalizable to those younger than 65 years" and adults with commercial or no health insurance.
The FDA "strongly believes" the benefits of COVID-19 vaccines outweigh the risks of infection, it said. The FDA is not taking any regulatory actions based on the findings because they require "more robust study," the report concluded.
Abou-Ismail said he has no concerns about the Pfizer vaccine causing blood clots as a result of this study.
"This study does not tell me much. There have been many other studies on mRNA vaccines that did not show this relationship," he said. "It is common for ‘weak’ studies to show conflicting results, which is why they cannot be used to determine causation."
An Instagram post claimed that the FDA said that the Pfizer vaccine causes blood clots.
The FDA did not say that. A study by FDA researchers of Medicare and Medicaid data showed that in four categories, including pulmonary embolism, there was a "modestly elevated risk" after the Pfizer COVID-19 vaccine in people ages 65 and over.
But the researchers said the early warning system does not prove causation from a vaccine to an outcome, and that more robust studies are underway to evaluate the findings.
We rate the claim False.
Instagram post, Dec. 17 2022
Vaccine, "Surveillance of COVID-19 vaccine safety among elderly persons aged 65 years and older," Dec. 1, 2022
U.S. Food and Drug Administration, "Initial Results of Near Real-Time Safety Monitoring of COVID-19 Vaccines in Persons Aged 65 Years and Older," July 12, 2021
Dr. Yazan Abou-Ismail, Twitter thread, Dec. 17, 2022
Dr. Yazan Abou-Ismail, email interview, Dec. 20, 2022
National Library of Medicine, "Risk of venous thromboembolism after COVID-19 vaccination," July 2022
National Library of Medicine, "No apparent association between mRNA COVID-19 vaccination and venous thromboembolism," November 2022
PolitiFact, "There’s no evidence linking COVID-19 vaccine to these athletes’ strokes, blood clots," Dec. 13, 2022
American Heart Association, "Blood clot risk remains elevated nearly a year after COVID-19," Sept, 19, 2022
Cedar Sinai, "New Data Show COVID-19 Vaccine Does Not Raise Stroke Risk," Aug. 24, 2022
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