Social Media Posts Misrepresent FDA’s COVID-19 Vaccine Safety Research

24.12.2022, 1:15, Разное
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SciCheck Digest

A vaccine safety surveillance study from the Food and Drug Administration has been misrepresented online. The paper did not establish a link between the Pfizer/BioNTech COVID-19 vaccine and blood clots, as some have claimed — and to date, other, more robust research has not identified such associations.

How do we know vaccines are safe?

How do we know vaccines are safe?

No vaccine or medical product is 100% safe, but the safety of vaccines is ensured via rigorous testing in clinical trials prior to authorization or approval, followed by continued safety monitoring once the vaccine is rolled out to the public to detect potential rare side effects. In addition, the Food and Drug Administration inspects vaccine production facilities and reviews manufacturing protocols to make sure vaccine doses are of high-quality and free of contaminants.

One key vaccine safety surveillance program is the Vaccine Adverse Event Reporting System, or VAERS, which is an early warning system run by the Centers for Disease Control and Prevention and FDA. As its website explains, VAERS “is not designed to detect if a vaccine caused an adverse event, but it can identify unusual or unexpected patterns of reporting that might indicate possible safety problems requiring a closer look.”

Anyone can submit a report to VAERS for any health problem that occurs after an immunization. There is no screening or vetting of the report and no attempt to determine if the vaccine was responsible for the problem. The information is still valuable because it’s a way of being quickly alerted to a potential safety issue with a vaccine, which can then be followed-up by government scientists.

Another monitoring system is the CDC’s Vaccine Safety Datalink, which uses electronic health data from nine health care organizations in the U.S. to identify adverse events related to vaccination in near real time.

In the case of the COVID-19 vaccines, randomized controlled trials involving tens of thousands of people, which were reviewed by multiple groups of experts, revealed no serious safety issues and showed that the benefits outweigh the risks.

The CDC and FDA vaccine safety monitoring systems, which were expanded for the COVID-19 vaccines and also include a new smartphone-based reporting tool called v-safe, have subsequently identified only a few, very rare adverse events. 

For more, see “How safe are the vaccines?”

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The Food and Drug Administration published an article in the journal Vaccine on Dec. 1 that described an early warning system for vaccine safety and noted that the system identified some potential safety signals for the COVID-19 vaccine from Pfizer/BioNTech that should be investigated further.

Among them were pulmonary embolisms, or blood clots in the lung, a condition that calls to mind one of the most commonly advanced claims made by anti-vaccination campaigners — the unfounded idea that COVID-19 vaccines are causing widespread death due to blood clots.

A couple of weeks after the article was published, the Epoch Times — a conservative outlet with a history of spreading dubious claims about the COVID-19 pandemic and vaccines — posted a misleading headline referencing that now-entrenched narrative, saying: “Pfizer’s COVID-19 Vaccine Linked to Blood Clotting: FDA.”

Then other outlets went even further. Conspiracy theorist Stew Peters, for example, posted a video that cited the Epoch Times story and claimed that “the FDA has finally admitted that Pfizer causes blood clots” and that this is “part of a mass genocide operation.”

One Facebook user shared the video with a message that said, “It’s why it’s called the ‘clot shot.’”

But all of these claims misrepresent the paper.

“The FDA has not found any new causal relationships between the Pfizer-BioNTech COVID-19 Vaccine and potential adverse events of special interest identified in 2021,” FDA spokeswoman Abby Capobianco said in an email to

“The FDA continues to find that the Pfizer-BioNTech COVID-19 Vaccine meets the FDA’s rigorous standards for safety and effectiveness and the agency strongly believes the potential benefits of COVID-19 vaccination outweigh the potential risks of COVID-19,” she said.

Here’s what the paper actually said: FDA researchers used a system drawing on data from the Centers for Medicare & Medicaid Services for more than 30 million elderly people — those who are 65 and older — to look at 14 ailments and track their incidence among recipients of the three available vaccines in the U.S. and then compare those numbers to a historical baseline for the incidence of those ailments.

The project didn’t investigate the cause of the potential safety signals, it only observed the frequency of certain health problems.

It found that four of the 14 ailments initially “met the threshold for a statistical signal” after COVID-19 vaccination with the Pfizer/BioNTech shot. None met the threshold following vaccination with the shots from either Moderna or Johnson & Johnson.

Then, after further evaluation, three of the initially flagged ailments — immune thrombocytopenia, disseminated intravascular coagulation and acute myocardial infarction — no longer met the statistical threshold, leaving only pulmonary embolism as a potential safety signal.

“Our new findings of statistical signals for four important outcomes for the [Pfizer] vaccine should be interpreted cautiously because the early warning system does not prove that vaccines cause the safety outcomes,” the researchers wrote. “FDA strongly believes the potential benefits of COVID-19 vaccination outweigh the potential risks of COVID-19 infection.”

Deeper epidemiological studies that account for factors such as age and nursing home residency are underway to further evaluate the potential safety signals, according to the paper.

As we’ve explained before, the mRNA vaccines — which include the shots from Pfizer and Moderna — have not been associated with any kind of clotting problem.

In March, Dr. John Su, a medical officer for the CDC’s Vaccine Safety Team, told us, “To date, CDC has detected no unusual or unexpected patterns of blood clots, such as deep venous thrombosis (DVT) and pulmonary embolism (PE) following immunization.”

The J&J vaccine, however, can cause a particular kind of clotting that also involves low levels of blood platelets. The condition is very rare, and the CDC has recommended the two mRNA vaccines over J&J’s, which has accounted for only a small minority of the vaccine doses administered in the U.S.

“There are very large population studies involving millions of people that show that there is no increase in risk with the Pfizer and the Moderna vaccines in terms of thrombosis,” Dr. Adam Cuker, a hematologist with expertise in blood clots at Penn Medicine told us in March. “So very, very clear evidence that those vaccines don’t cause clots.”

And that remains true now. A review published in November that looked at all the available research on the question of mRNA vaccines and clots, which included “six robust studies including analysis of over 27 million doses of mRNA vaccines,” found that “the consistent result is that mRNA vaccines are not statistically associated with [venous thromboembolism],” or clots that form in veins.

And, actually, vaccination against COVID-19 could help to prevent blood clots, since it can prevent infection with the virus that can cause clotting, as we’ve explained before.

A person is much more likely to get a blood clot after being infected with COVID-19 than they are to get a clot after being vaccinated, Allison Burnett, president of the Anticoagulation Forum — an organization that works with health care providers to improve patient care — told us in September.

“So the message is — get vaccinated to avoid blood clots,” since getting infected can increase the risk of clots, she said.

The FDA isn’t “taking any regulatory actions” based on the findings of the recent paper because the signals are still under investigation and “require more robust study,” the researchers wrote.

“The statistical signals of four serious outcomes are not necessarily causal and may be due to factors potentially unrelated to vaccination,” they wrote.

“For example, the elderly Medicare population that received the [Pfizer/BioNTech] vaccine differed from other elderly COVID-19 vaccinated populations, including a preponderance of nursing home residents and populations with a higher comorbidity burden,” they wrote.

When we asked Pfizer for comment on the claims circulating about the FDA’s paper, a spokesperson told us that the company takes seriously any adverse events reported after vaccination with its shots.

“It is important to understand, however, that the [adverse events] reported may not have any causal relationship to the vaccine. Rather, the event may be due to an underlying disease or some other factor such as past medical history or concomitant medication or the [adverse events] may be coincidental,” the spokesperson said in an emailed statement.

So, anyone suggesting that this paper has “admitted” or established that the COVID-19 vaccine from Pfizer causes blood clots is wrong.

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