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Well before COVID-19 existed, the CDC had tweeted out warnings about blood clots.
Blood clots are common, affecting about 900,000 Americans each year, and can be deadly.
There is not an increased risk of blood clots from the Pfizer and Moderna COVID-19 vaccines.
Johnson & Johnson’s vaccine, the only other COVID-19 vaccine used in the U.S., has been linked to rare cases of thrombosis with thrombocytopenia syndrome (TTS).
A few days before Super Bowl LVI , the Centers for Disease Control and Prevention referenced the game in a tweet about how to safeguard against the common risk of blood clots.
"Normalizing blood clots," read a Feb. 12 Facebook post that shared a screenshot of the CDC tweet from two days prior. "Maybe, if you avoid a certain strongly pushed jab you won’t have to worry so much about this. & if you get CO\/ID you can take aspirin or NAC. Have they EVER before put out anything like this for the SuperBowl? The answer would be NO."
The 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 Facebook.)
The pre-Super Bowl tweet, however, was not the first time the CDC took to Twitter to warn about the dangers of blood clots. We found instances of such tweets published in February and March of 2015, years before there was a COVID-19, as well as twice in October of 2020, before there was an authorized COVID-19 vaccine in the U.S.
Neither was it the first time the CDC tied such a warning to a big sporting event. In 2016, it also warned its Twitter followers during March Madness about the dangers of blood clots.
The CDC did not return a request for comment for this article.
Blood clots are normal and are the body’s way of stopping bleeding after an injury. Those clots normally dissolve on their own and are harmless. But venous thromboembolism, which refers to clots that form in the veins, can be deadly. VTE consists of deep vein thrombosis (clots that usually begin in the legs but sometimes in the arm or pelvis) and pulmonary embolism (when a deep-vein clot dislodges and travels to the lungs).
The CDC says these types of blood clots affect about 900,000 people yearly in the U.S. and that about 100,000 people die from them. It’s the leading cause of death in people with cancer, aside from the cancer itself. It also is a leading cause of death in pregnant women or those who have just given birth.
Blood clots can happen to anyone, even athletes, but there are risk factors, including injuries, surgery, chronic illnesses, obesity and extended periods of limited movement, such as during long flights.
The Pfizer and Moderna vaccines were first authorized for emergency use in December 2020 and the Johnson & Johnson vaccine was given emergency authorization in February 2021.
There have been some reports of people developing blood clots after COVID-19 vaccination, but they are very rare.
According to the CDC and the FDA, there have been 57 confirmed reports of people who received the Johnson & Johnson vaccine and later developed a rare clotting disorder called thrombosis with thrombocytopenia syndrome (TTS). That’s out of more than 18 million doses given in the U.S., as of Feb. 3.
There have been nine deaths related to TTS among Johnson & Johnson vaccine recipients, according to the CDC. It recommends the Pfizer and Moderna vaccines instead, although it said the Johnson & Johnson vaccine can still be offered.
There have been three confirmed cases of TTS among Moderna vaccine recipients out of more than 522 million doses, according to the CDC, which said that there is not an increased risk of TTS from the vaccine.
The COVID-19 vaccine developed by AstraZeneca and Oxford University has also been tied to a rare blood clot disorder. Scientists believe they have figured out the cause: its use of another harmless virus that can leak into the bloodstream and bind to a protein that is involved in the natural clotting process, The New York Times reported. The AstraZeneca vaccine has not been authorized for use in the U.S.
Health experts say that patients who are infected with COVID-19 commonly develop blood clots due to the virus.
The virus "is very well known to cause blood clots, so your odds of getting COVID-induced blood clots if you catch COVID are higher than the vaccine induced blood clots," Dr. Shruti Gohil, associate medical director for epidemiology and infection prevention and assistant professor of infectious diseases, at the University of California, Irvine, School of Medicine, told PolitiFact in October.
The SARS-CoV-2 infection causes high levels of inflammation, which could trigger clotting often seen in COVID-19 patients, according to the National Heart Blood and Lung Institute.
A Facebook post expressing skepticism about the safety of the COVID-19 vaccines claimed the CDC was "normalizing blood clots" by tweeting about it before the Super Bowl.
Blood clots are common and can kill up to 100,000 Americans a year. The CDC has previously tweeted about the dangers of blood clots, including during the 2016 NCAA college basketball tournament.
The Johnson & Johnson vaccine has been linked to rare cases of TTS, and the CDC said people should get the Pfizer and Moderna instead. Another vaccine from AstraZeneca, which has not been authorized for use in the U.S., has been linked to a separate, rare clotting disorder.
Meanwhile, people are at risk of developing blood clots from the COVID-19 infection itself, which causes inflammation in the body.
The post is wrong to suggest that the CDC’s warning about blood clots is a new thing and that it’s somehow tied to COVID-19 vaccines.
We rate this claim False.
American Heart Association, "What is Venous Thromboembolism (VTE)?"
American Society of Hematology, "Blood Clots"
CDC, "Venous Thromboembolism (Blood Clots)"
CDC, "Selected Adverse Events Reported after COVID-19 Vaccination," Feb. 7, 2022
CDC, "Johnson & Johnson’s Janssen COVID-19 Vaccine Overview and Safety," Dec. 28, 2021
National Institutes of Health, "Blood Clots Explained," May 2021
National Heart Lung and Blood Institute, "COVID-19 and the Blood," Nov. 3, 2021
PolitiFact, "No evidence that Pfizer COVID-19 vaccine causes blood clots," Oct. 29, 2021
PolitiFact, "No clear evidence that COVID vaccines are responsible for strange blood clots observed by embalmers," Feb. 9, 2022
PolitiFact, "Blood clots associated with COVID-19 vaccine are extremely rare," Oct. 20, 2021
PolitiFact, "Clots, heart problems from COVID-19 vaccines rare; deaths from the virus persist," Dec. 10, 2021
The New York Times, "Scientists say they may have found the way AstraZeneca’s vaccine can cause rare blood clots," Dec. 2, 2021
Weill Cornell Medicine, "Blood Clots: Extremely Common But Rarely Related to the COVID-19 Vaccine," July 14, 2021
University of Chicago Medicine, "UChicago Medicine doctors report an increased risk of blood clots in patients with COVID-19," April 27, 2021
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