Social media post appears to overstate risk of vaccine blood clots

14 October 2021
What was claimed

The risk of a blood clot following a Covid-19 vaccine is worse than the cold or flu symptoms you may experience if infected.

Our verdict

This overstates the risk of blood clots caused by the vaccine. Furthermore, evidence suggests the risk of clotting and other arterial conditions is much higher following infection than vaccination.

A post on Facebook appears to compare reported Covid-19 vaccine side effects with mild symptoms of the virus itself. Although it doesn’t explicitly mention Covid-19 vaccination, the post seems to weigh up the pros and cons, claiming that “society” is “willingly choosing blood clots and heart problems over cold and flu symptoms or no symptoms at all”. The caption attached to the post adds: “Not worth the risk at all.”

This misleadingly suggests that the risks of the Covid-19 vaccine outweigh the benefits. In fact, the volume of reported side effects is extremely small when compared to the number of people who have received one or both doses of the vaccine, and studies have shown vaccination is extremely effective at preventing the most serious side effects. 

Moreover, while there are some similarities between the flu and Covid-19, the fatality rate of Covid-19 is thought to be higher. 

What is the risk of blood clots and heart problems?

The risk of blood clots following a Covid-19 vaccine is extremely small. Government estimates for the AstraZeneca vaccine (which has been most closely associated with this risk) suggest that for those over the age of 40 it is around 1 in 100,000 doses, while it is around 1 in 50,000 among those aged 18 to 39 . 

According to the Medicines and Healthcare products Regulatory Agency (MHRA) Yellow Card scheme (which is used to actively monitor drug and health product safety) there have been 72 reports of fatalities in the UK after suspected blood clots and low platelets following use of the AstraZeneca vaccine. 

Rates of clotting and death following the use of Pfizer and Moderna are lower (two reports of deaths in the UK following use of the Pfizer vaccine and none for Moderna). 

The MHRA cautions that many of the events it records occur by chance and are not necessarily a result of the vaccine, which is why the reports are described as “suspected reactions”. 

The MHRA and the Joint Committee on Vaccination and Immunisation (JCVI) still say that despite these reports the benefits of the vaccine outweigh the risks involved for the majority of people (although the JCVI has said it is “preferable” that under-40s without underlying health conditions be offered an alternative vaccine to AstraZeneca if they have not yet been vaccinated).

And while reports of clotting should be noted, the number of these reports are in stark contrast to the 94 million doses of vaccines (both first and second) delivered in the UK

The risk of clotting appears higher after infection than vaccination

There is also evidence which suggests the risk of clotting after infection with Covid-19 is greater than after vaccination. 

An analysis by the University of Oxford of 29 million people in England compared the risk of hospitalisation or death from blood clots after first doses of the AstraZeneca or Pfizer vaccines, and after Covid-19 infection. It found that while there was an increase in the risk of blood clots and other vascular events “observed for short time intervals after first doses” of both the Pfizer and AstraZeneca vaccines, it was also the case that “risks of most of these events were substantially higher and more prolonged after SARS-CoV-2 infection than after vaccination”.

Similarly, while there is a risk of myocarditis (an inflammation of the heart) following vaccination, it is both a rare side effect and, according to new research, also more likely following infection from Covid-19 than following vaccination. 

Comparing Covid-19 with cold and flu is misleading 

The suggestion that Covid-19 may amount to “cold and flu symptoms” is also misleading. While there are some similarities in symptoms, Covid can also cause much more serious illness. There is also some evidence to suggest that Covid-19 may be more deadly than flu, particularly among those who haven’t been vaccinated. 

As we’ve said when we have written about this before, the risk of dying after contracting flu is hard to pin down. Some estimates from New Zealand (which vaccinates a similar proportion of its elderly against the flu to the UK) put it at around 0.04% of cases, while data from the US Centers for Disease Control and Prevention shows that around 0.1%-0.2% of symptomatic flu cases result in death.  

Without vaccination the risk of dying once infected with Covid-19 is estimated to be between 0.5% to 1% on average (although death rates have been affected by the rollout of vaccines and may also improve as new treatments become available). 

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 missing context because it appears to overstate the risk of blood clots caused by vaccines and evidence suggests you are at greater risk of blood clots or heart problems from being infected with Covid-19 than being vaccinated for it.

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