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.
The study’s limitations
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.
What it means
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."
He pointed to other recent studies that showed no risk of venous thromboembolism after COVID-19 vaccination.
Meanwhile, recent studies have shown an increased risk of blood clots from contracting the COVID-19 virus.
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.