Fact check: No definitive link between AstraZeneca’s COVID-19 vaccine and blood clot incidents

The claim: AstraZeneca’s COVID-19 vaccine causes blood clotting disorders

On March 11, President Joe Biden announced an ambitious initiative to bring the U.S. closer to a pre-pandemic normalcy: making every adult vaccine-eligible before the summer. 

“Tonight, I’m announcing that I will direct all states, tribes, and territories to make all adults — people 18 and over — eligible to be vaccinated no later than May 1,” he said during his presidential address marking the one-year anniversary of the COVID-19 pandemic.  

But no less than a week later, reports of blood clots following vaccination with the AstraZeneca-Oxford vaccine — one of four COVID-19 vaccines available globally albeit not in the U.S. — have many on social media linking the two. 

“Google ‘Ireland AstraZeneca Blood Clot’ and ask yourself why America’s media isn’t announcing this,” claims one March 14 Facebook post.

“We are experiencing the greatest test in human history,” claims another post from March 16 alongside a graphic mentioning European countries that have allegedly ceased AstraZeneca vaccine distribution.

“Looks like the sideeffects (sic) were not just ‘a conspiracy theory’” the graphic concludes. 

“Let me help you with that headline,” writes British media personality Katie Hopkins in a March 12 Instagram post sharing a screenshot of a headline describing Italy, Norway and Denmark’s halting of AstraZeneca’s vaccine. “Experimental injectable canned after young woman drops dead and others end up in intensive care.” 

USA TODAY has reached out to the posters for further comment. 

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What exactly happened with the vaccine? 

In early March, reports of blood clots, abnormal bleeding and low blood platelets (the part of blood that assists clotting, especially during injury) following vaccination cropped up across Europe, leading more than 20 countries to temporarily suspend the AstraZeneca vaccine’s roll-out as a safety precaution.

Scientists and experts in the U.S. admonished the move, saying suspensions before investigations did more to harm the vaccination rollout, given the lack of clear-cut data, and ultimately undermine the global coronavirus recovery effort.   

According to the European Union’s regulatory authority, the European Medicines Agency, there have been 30 cases reported since March 10 among almost 5 million people vaccinated with AstraZeneca’s vaccine in the European Economic Area, which comprises of member EU states and countries with trade agreements.

Some cases involved blood clots in the lungs, or pulmonary embolism, but others involved deep vein thrombosis, or DVT, a blood clot in the legs; disseminated intravascular coagulation, or DIC, blood clots throughout the blood; and in rarer instances, central venous sinus thrombosis, or CVST, a blood clot in the veins of the brain preventing blood from leaving.

While some individuals recovered, a few others did not.

One 50-year-old Italian man is reported to have died after developing DVT following vaccination. A 60-year-old Danish woman, with an “unusual clinical picture” according to the Danish Medicines Agency, died after developing DIC. A 49-year-old Austrian woman, a nurse, died as a result of a “severe coagulation disorder,” according to Reuters. 

In Germany, health officials received seven reports of CVST, three of which were fatal; in the U.K., one individual, among five reported of CVST, died. 

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EMA rules out AstraZeneca’s vaccine

On March 18, the EMA announced AstraZeneca’s vaccine didn’t appear to increase the overall occurrence of blood clots and that its benefits “continue to outweigh the rise of side effects.”

While the agency stated there was some concern for younger people – the EMA found most reports of DIC and CVST occurred in women under 55 – particularly when it came to the rare blood clotting disorders, it concluded that the overall number of blood clotting cases since the rollout were lower than expected in the general population based on pre-COVID figures. 

Countries across Europe resumed vaccination with AstraZeneca’s vaccine on March 19. The EMA stated it would closely monitor vaccine recipients to see if reports of blood clotting events continue.   

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On March 22, AstraZeneca and the University of Oxford released interim results from their over 32,000-person vaccine trial in the U.S., Peru and Chile. The results showed the vaccine conferred strong protection against COVID-19 across all age groups, health status, ethnicity and race. It also reported no severe safety issues, like blood clots, or other serious side effects.

Replying to concerns raised by the National Institute of Allergy and Infectious Diseases on March 23 of “outdated information from that trial,” AstraZeneca said while its results were based on interim analysis of data before Feb. 17, “preliminary analysis” of final results were consistent with the earlier data.

Vaccines don’t cause blood clots

It’s important to note vaccines have not been shown to cause blood clots, according to Dr. Daniel Salmon of Johns Hopkins’ Institute for Vaccine Safety to the New York Times in March.

“There are a lot of causes of blood clotting, a lot of predisposing factors, and a lot of people who are at increased risk – and these are often also the people who are being vaccinated right now,” said Dr. Mark Slifka, a vaccine researcher at Oregon Health and Science University, also to the Times.

COVID-19 can instigate blood clots, and there’s some thought undetected infection before vaccination could be an underlying factor, at least for the more severe cases of blood clotting.

In rare instances, lowered blood platelets have been observed with some vaccines, particularly with the measles, mumps and rubella vaccine, according to the U.S. Centers for Disease Control and Prevention. But the effect is temporary and any bleeding disorders that result usually resolve with treatment.  

In January, a Florida doctor died from a hemorrhagic stroke after receiving the Pfizer-BioNTech vaccine. His death has been linked to a rare and unusual bleeding disorder called immune thrombocytopenia, or ITP, caused by low platelet levels. Since then, there have been 36 other cases of ITP among both Pfizer and Moderna vaccine recipients reported to Vaccine Adverse Event Reporting System, The New York Times reported in early February. All these cases, including the death of the Florida doctor, are still under investigation.

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Our ruling: Missing context 

We rate this claim MISSING CONTEXT because without additional context it might be misleading. In early March, reports of cases involving blood clots, abnormal bleeding and low blood platelets – a few fatal – led many European countries to temporarily suspend AstraZeneca-Oxford’s COVID-19 vaccine, which is not available in the U.S. The European Union’s drug regulatory agency, European Medicines Agency, later said the vaccine did not increase the overall incidence of blood clots and that the benefits of using it outweighed the possible risks. Vaccines are not known to cause blood clots although there have been cases of immune thrombocytopenia, a rare condition marked by low platelets, following vaccination with Moderna’s and Pfizer’s COVID-19 vaccines. Whether there is an actual connection is still under investigation and will be closely monitored as vaccination with AstraZeneca’s vaccine resumes.

Our fact-check sources:

• USA TODAY, March 11, “Takeaways from Biden’s speech: Small gatherings by July 4, denouncing racist attacks and a contrast to Trump“
• C-SPAN, March 11, “Presidential Address on One-Year Anniversary of Coronavirus Pandemic“
• University of Rochester Medical Center, accessed March 18, “What Are Platelets?“
• USA TODAY, March 17, “‘It’s easy to scare people’: Europe’s decision to pull AstraZeneca-Oxford vaccine threatens global COVID-19 recovery efforts, US experts say“
• European Medicines Agency, March 11, “COVID-19 Vaccine AstraZeneca: PRAC investigating cases of thromboembolic events – vaccine’s benefits currently still outweigh risks – Update” 
• Mayo Clinic, June 13, 2020, “Pulmonary embolism” 
• MedlinePlus, Feb. 26, “Disseminated intravascular coagulation (DIC)“
• Mayo Clinic, Dec. 22, 2020, “Deep vein thrombosis (DVT)” 
• Johns Hopkins Medicine, accessed March 18, “Cerebral Venous Sinus Thrombosis (CVST)” 
• Reuters, March 15, “Italy prosecutors seize batch of AstraZeneca vaccine after death of man” 
• Danish Medicines Agency, March 14, “Danish Medicine Agency clarifies information on the death reported in Denmark after vaccination with the AstraZeneca vaccine“
• Reuters, March 7, “Austria suspends AstraZeneca COVID-19 vaccine batch after death“
• Science, March 17, “‘It’s a very special picture.’ Why vaccine safety experts put the brakes on AstraZeneca’s COVID-19 vaccine” 
• Reuters, March 18, “UK reports five cases of rare blood clots in 11 million AstraZeneca shots, continues with vaccine” 
• European Medicines Agency, March 18, “COVID-19 Vaccine AstraZeneca: benefits still outweigh the risks despite possible link to rare blood clots with low blood platelets” 
• Associated Press, March 19, “AstraZeneca vaccinations resume in Europe after clot scare” 
• USA TODAY, March 22, “AstraZeneca says US data shows COVID-19 vaccine prevents 79% of symptomatic disease” 
• National Institutes of Health, March 23, “NIAID Statement on AstraZeneca Vaccine“
• AstraZeneca, March 23, “Update following statement by NIAID on AZD1222 US Phase III trial data”  
• The New York Times, March 22, “Should You be Concerned About Blood Clots, Bleeding and the AZ-Vaccine?“
• Science News, Nov. 2, 2020, “How COVID-19 may trigger dangerous blood clots” 
• U.S. Centers for Disease Control and Prevention, Sept. 9, 2020, “Measles, Mumps, Rubella (MMR) Vaccine” 
• USA TODAY, Jan. 10, “Death of Florida doctor after receiving COVID-19 vaccine under investigation” 
• Mayo Clinic, April 30, 2019, “Immune thrombocytopenia (ITP)“
• The New York Times, Feb. 10, “A Few Covid Vaccine Recipients Developed a Rare Blood Disorder”  

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