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SciCheck’s COVID-19/Vaccination Project

Misleading Claims on Well-Known Rare Risk of AstraZeneca COVID-19 Vaccine

This article is available in both English and Español

SciCheck Digest

A rare risk of dangerous blood clots associated with the AstraZeneca COVID-19 vaccine was identified and reported in early 2021. This month, the company announced it was pulling the vaccine off the market globally, citing a decline in demand. Social media posts misleadingly linked the decision to the company having “admitted” the rare side effect “for the first time” in court documents and used it to impugn all vaccines.

Full Story

The association between the AstraZeneca COVID-19 vaccine and a rare and dangerous blood clotting condition combined with low blood platelets has been known for more than three years. The condition is known as thrombosis with thrombocytopenia syndrome, or TTS, in general, and vaccine-induced thrombotic thrombocytopenia, or VITT, when it implies an association to vaccines.

The European Medicines Agency, which regulates vaccines in the European Union, first warned of the possible link between the vaccine and “very rare cases of blood clots associated with thrombocytopenia, i.e. low levels of blood platelets” on March 18, 2021. In a statement issued that same day, the pharmaceutical company acknowledged the finding and said it “recognises and will implement” EMA’s recommendations, including updating the product information to warn about the reported cases.

A few weeks later, in April 2021, the EMA concluded the unusual blood clots “should be listed as very rare side effects” of the vaccine. TTS is included in the “possible side effects” section in the package leaflet for users for Vaxzevria (page 30), one of the brand names of the vaccine along with Covishield. TTS has also been listed in Covishield’s product insert under the “special warnings” section, as a side effect in the fact sheet for recipients since at least August 2021, and as a possible adverse reaction in an FAQ page from its manufacturer that was updated on July 5, 2021.

In September 2021, the National Health Service in England reported that the “rare condition” affected approximately 1 in 50,000 AstraZeneca COVID-19 vaccine recipients under 50 years old and 1 in 100,000 recipients older than 50. Between May 2021 and May 2022, there were 443 cases of TTS reported following vaccination in the U.K.; 81 of them were fatal. (In July 2021, the vaccine was also linked to rare cases of Guillain-Barré syndrome, a neurological disorder that leads to muscle weakness and, at times, paralysis. The World Health Organization said that most people recover fully.) 

The vaccine was never used in the U.S. outside clinical trials — AstraZeneca decided not to file the application for approval. But the vaccine was widely used in the rest of the world, especially during 2021. 

In March, the European Commission withdrew AstraZeneca’s authorization to market its COVID-19 vaccine in the European Union, at the company’s request, and on May 7, the company announced it was pulling the vaccine from the market globally. Social media posts misleadingly framed the company’s recent decision as a consequence of “admitting” the rare TTS condition “for the first time” in court documents, as part of a lawsuit in the U.K. The claim was also shared in Spanish.

AstraZeneca had said the decision was based on a decline in demand. Other COVID-19 vaccine manufacturers had developed new versions to target variants of the virus that causes COVID-19. “As multiple, variant COVID-19 vaccines have since been developed there is a surplus of available updated vaccines,” the company said in a statement sent to us.

“AstraZeneca finally WITHDRAW Covid vaccine worldwide, months after the pharmaceutical giant admitted for the first time in court documents that it can cause ‘a rare and dangerous’ side effect. Never forget how they cancelled anyone who questioned its safety,” reads a viral post shared across social media platforms.

The U.K. news website the Telegraph had reported on April 28 that AstraZeneca had “admitted” its COVID-19 vaccine could cause TTS “in an apparent about-turn that could pave the way for a multi-million pound legal payout” in a class action lawsuit in which the company is being sued for “death and serious injury in dozens of cases.” The article said the company hadn’t said that in a court document before. But the story went on to say that a link between the vaccine and the rare blood clotting condition was identified in March 2021, as we said. 

On May 7, the Telegraph reported that AstraZeneca was “being withdrawn worldwide, months after the pharmaceutical giant admitted for the first time in court documents that it can cause a rare and dangerous side effect.” The next day, the Independent, a British online newspaper, published a story with the headline “AstraZeneca withdraws Covid vaccine worldwide after admitting it can cause rare blood clots.”

Christina Pagel, professor of operational research at University College London, said the headlines were “needlessly scary” on her blog on May 8, and days later in an op-ed with Sheena Cruickshank, immunologist at the University of Manchester, in the New Statesman, a U.K. publication.

“Fundamentally, the situation is this: there isn’t a new ‘smoking gun’; the AZ vaccine was one of the first and cheapest vaccines; it saved millions of lives globally; and there are better vaccines out there now, adapted to new variants,” they wrote.

AstraZeneca’s COVID-19 Vaccine Safety and Impact 

Even though the rare risk associated with the AstraZeneca COVID-19 vaccine was reported early on and was well-known, some social media users took the Telegraph’s news reports as vindication

“Now they admit it,” wrote conservative commentator Dan Bongino in a Facebook post, linking to a Rumble video titled “AstraZeneca Makes SHOCKING Admission About COVID Vax – We Were Right All Along.” 

Others used the apparent news to cast shade on all other COVID-19 vaccines. “It’s not just the Astra Zeneca,” one Facebook post said. 

A commenter to a post on Instagram wrote, “Whens the class action lawsuit against the US Government?,” although the vaccine was not authorized for use in the U.S. Another one wrote, “When will Pfizer finally step up and do the same?,” although the Pfizer/BioNTech COVID-19 vaccine has not been linked to TTS.

Just like other COVID-19 vaccines authorized or approved for use, the AstraZeneca COVID-19 vaccine, co-developed by Oxford University, was found to be safe and effective for people over 18 years old in clinical trials and in further studies. The efficacy of the vaccine in preventing symptomatic disease in clinical trials was 74%, which was lower than its mRNA counterparts, namely the Pfizer/BioNTech and Moderna vaccines.

Vials of the AstraZeneca COVID-19 vaccine. Photo by Leon Neal via Getty Images.

After the potentially deadly blood clot side effect was identified in 2021, many countries restricted the AstraZeneca vaccine use for only older populations. The reported TTS cases were more prevalent among those younger than 50. 

Because AstraZeneca’s vaccine was cheaper and easier to distribute than other COVID-19 vaccines, it was among the first vaccines sent to poorer countries by COVAX, a global initiative that allowed for equitable access to COVID-19 vaccines. 

Since its rollout, more than 3 billion doses were distributed in over 180 countries, according to a 2022 statement from the vaccine developers, with approximately two-thirds of the doses going to poorer countries. A 2022 analysis by Airfinity, a disease-forecasting company, showed that the vaccine saved 6.3 million lives from December 2020 to December 2021. The company used data from a study by scientists with the Imperial College London on the global impact of COVID-19 vaccination during that year.

Vaccines in the U.S.

As we said, the AstraZeneca COVID-19 vaccine was not used in the U.S. outside clinical trials.

The Johnson & Johnson COVID-19 vaccine, though, uses the same platform as the AstraZeneca vaccine. Both use a modified, harmless adenovirus, a type of virus that typically causes the common cold, to trigger an immune response. The J&J vaccine was granted an emergency use authorization in February 2021, but soon after, in April of that year, the Food and Drug Administration and the Centers for Disease Control and Prevention reported cases of TTS following the administration of the vaccine and recommended a “pause” in its use. The FDA also reported rare cases of GBS in July 2021.

The FDA limited the authorization of the J&J vaccine to certain people in May 2022, and the vaccine was ultimately discontinued in 2023. As of April 7, 2022, the CDC and FDA had confirmed 60 cases of TTS, including nine deaths, among more than 18.6 million J&J vaccines administered. In September 2023, the CDC said TTS after J&J COVID-19 vaccination “has occurred in approximately 4 cases per one million doses administered.”

The first two COVID-19 vaccines authorized and approved in the U.S., the Pfizer/BioNTech and Moderna vaccines, are both mRNA vaccines. The mRNA COVID-19 vaccines were widely used in the U.S., and neither has been linked to TTS. For context, as of April 26, 2023, approximately 367 million doses of the Pfizer/BioNTech vaccine, 232 million doses of the Moderna vaccine and 19 million doses of the J&J vaccine had been administered in the country.

Both mRNA vaccines have been shown to be safe, with rare serious side effects reported, and effective at preventing severe COVID-19 disease and death. One estimate published in December 2022 suggests that COVID-19 vaccines prevented more than 18 million hospitalizations and 3 million deaths in the U.S. 

Editor’s note: SciCheck’s articles providing accurate health information and correcting health misinformation are made possible by a grant from the Robert Wood Johnson Foundation. The foundation has no control over FactCheck.org’s editorial decisions, and the views expressed in our articles do not necessarily reflect the views of the foundation.


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