Unevidenced claims about the AstraZeneca vaccine on social media

25 March 2021
What was claimed

The Astrazeneca vaccine in the UK causes blood clots.

Our verdict

The AstraZeneca Covid-19 vaccine is not associated with an increased overall risk of blood clotting disorders. There have been a small number of cases of a rare type of blood clot following vaccination. It is not clear whether this is linked to the vaccine or not, and this is being closely monitored by regulatory bodies.

While this article was correct at the time it was first published, the evidence regarding a possible association between blood clots and the AstraZeneca vaccine has moved on, and the guidance from the Medicines and Healthcare products Regulatory Agency and European Medicines Agency has been updated.  Our piece on the evidence and guidance around the AstraZeneca vaccine can be found here. 

This article has been archived as a result. You can find our latest fact checks on Covid-19 here.

A video of a Sky News segment has been shared on social media by a group called ‘Mysteries, Truths, and Conspiracies’, with the caption: “UK jabs causing blood clots, but denied as you would expect”. This caption is false.

 As of mid-March, when the post was published, there was not sufficient evidence to say that the AstraZeneca vaccine has caused blood clots. It is not clear if the post is suggesting that Sky News is denying it’s claim about the blood clots, or that its reporting on blood clots is being denied by others. Both are incorrect.

 The Sky News video discusses some cases of people who have had blood clots around the time of vaccination, and the precautionary action taken by some European (and some non-European) countries.  It clearly says that these occurrences are not happening more frequently in vaccinated people than they would normally in the general unvaccinated population. 

In fact, during the video, science correspondent Thomas Moore, says: "There’s no increased rate of blood clots following vaccination. Experts say the European reaction has been disproportionate". 

He ends the report saying: “There’s nothing to suggest a causal link between clots and the vaccine, so there seems no reason to be worried about either vaccine being used in the UK roll out.”


Where does the controversy about the AstraZeneca vaccine and blood clots come from?

We have written about this topic before

Due to reports of people developing blood clots close to the time of vaccination, in March, some countries temporarily suspended their vaccination programmes as a precautionary measure. 

Up until the 10th March 2021—the week of the suspensions—30 cases of “thromboembolic events” (formation of a blood clot in a blood vessel) had been reported in the five million people who had received the AstraZeneca vaccine in the European Economic Area (all EU member states, plus Iceland, Liechtenstein and Norway).

The normal occurrence of blood clots in the general population (unvaccinated) is 1 in 1000, and likely higher in older age groups, and so as described by the European Medicines Agency (EMA), this number was no higher than we might normally expect. 

It said: “The number of thromboembolic events overall in vaccinated people seems not to be higher than that seen in the general population.”

A rough estimate, calculated by Professor David Spiegelhalter, chair of the Winton Centre for Risk and Evidence Communication at Cambridge University, demonstrated that we’d expect roughly about 100 people a week to have issues with blood clots, which is far more than the 30 seen over a month or so following the AstraZeneca vaccine.

The EMA has since reviewed the data and issued information for patients, saying the AstraZeneca vaccine is “not associated with an increased overall risk of blood clotting disorders” and described the cases of “unusual blood clots accompanied by low levels of blood platelets” after vaccination as “very rare”.

“Because COVID-19 can be so serious and is so widespread, the benefits of the vaccine in preventing it outweigh the risks of side effects”, the EMA said.

The UK regulatory body, The Medicines and Healthcare Products Regulatory Agency (MHRA) also released a statement on 18 March saying that the “available evidence does not suggest that blood clots in veins (venous thromboembolism) are caused by COVID-19 Vaccine AstraZeneca.” 

The MHRA said a further review of “five reports of a very rare and specific type of blood clot in the cerebral veins (sinus vein thrombosis) occurring together with lowered platelets” is ongoing, but added that a “causal association with the vaccine has not been established”.

It added: “The MHRA’s advice remains that the benefits of the vaccines against COVID-19 continue to outweigh any risks and that the public should continue to get their vaccine when invited to do so.”

Update 7 April 2021

This piece was updated to include mention of the ongoing monitoring of any link between the vaccine and rarer types of blood clots.

Update 13 April 2021

We have updated this article to reflect the lack of clarity around the intended meaning of part of the Facebook post.

This article is part of our work fact checking potentially false pictures, videos and stories on Facebook. You can read more about this—and find out how to report Facebook content—here. For the purposes of that scheme, we’ve rated this claim as false because the statement from the European Medicines Agency has said “the AstraZeneca COVID-19 Vaccine is not associated with an increased overall risk of blood clotting disorders.”

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