No evidence that Pfizer COVID-19 vaccine causes blood clots

An Instagram post that uses excerpts from an interview on Infowars, a conspiracy oriented website run by Alex Jones, claims that Pfizer’s COVID-19 vaccine causes blood clotting "in a minute or two."

In the interview, a doctor says he added the Pfizer vaccine to human blood and that, using a microscope, within "a minute or two, you see the blood starts to clot."

Excerpts from the interview were shared in an Instagram post that was flagged as part of Facebook’s efforts to combat false news and misinformation on its News Feed. (Read more about our partnership with Facebook.)

There is no evidence that the Pfizer vaccine causes blood clots.

"I am not aware of any causally related clotting problem with either" the Pfizer or the Moderna vaccines, which are known as  mRNA vaccines, said Dr. Walter Orenstein, a professor in the infectious diseases division at Emory University’s School of Medicine and associate director of the Emory Vaccine Center. "I am also not aware of any information published in the medical literature about clotting problems with the mRNA vaccines."

We previously reported that a serious syndrome involving blood clots known as TTS is associated with the third COVID-19 vaccine being administered in the United States, the Johnson & Johnson vaccine. The federal Centers for Disease Control and Prevention says there is a "plausible causal relationship" between that vaccine and TTS.

The phenomenon is exceedingly rare: More than 15 million doses of the Johnson & Johnson vaccine have been given in the U.S., with 47 confirmed reports of people who later developed TTS.

​​No increased risk of TTS has been detected with the Pfizer and Moderna vaccines, according to the CDC.

Featured Fact-check

Viral image

stated on October 15, 2024 in a Threads post

Photo shows Vice President Kamala Harris and Sean “Diddy” Combs.

The messenger RNA, or mRNA, technology used to create the Moderna and Pfizer vaccines use the human body’s natural immune response to their advantage. The shots give cells the directions for how to make a harmless spike protein. Such spike proteins are found on the surface of the virus that causes COVID-19 — and it is these proteins that the virus uses to bind to cells. The immune system of a person who receives the mRNA vaccine then spots the unknown protein and makes antibodies to fight it. 

Dr. Shruti Gohil, professor of infectious diseases at the University of California, Irvine, School of Medicine, noted that "platelets and other clotting factors are naturally in our blood to help us stop bleeding when we get injured, so blood clots very easily naturally, unless you do something to make it not clot.

"For example, even exposure to air will make your blood clot.  In fact, when we draw blood for testing we have to have special tubes with chemicals in them to keep your blood from clotting."

But there is no indication that the Pfizer vaccine triggers any action that results in blood clots.

We rate the Instagram post False.