The chance of being killed by a cow and other AstraZeneca vaccine risk comparisons explained

On Wednesday the Medicines and Healthcare products Regulatory Agency (MHRA) said the likelihood of getting a blood clot after a dose of the Oxford-AstraZeneca Covid-19 vaccine is approximately four in a million. 

Of the 79 cases reported to the MHRA, 19 patients had died. This has been reported as a one-in-a-million risk of dying from a blood clot after having a dose of the AstraZeneca vaccine. 

In a bid to reduce public anxiety about the MHRA’s announcement, some news outlets have compared these likelihoods to other statistically extremely unlikely events, such as being killed by a cow or having your home hit by a plane falling from the sky. 

We’ve taken a look at some of the claims. 

The chance of dying of a blood clot after the AstraZeneca vaccine is almost the same as being killed by a cow 

In a Q&A section of Thursday’s paper, The Sun claimed that “you are almost as likely to be killed by a cow” as you are to develop a serious blood clot from the vaccine. It said being killed by a cow had a likelihood of one in 300,000, compared to one in 250,000 for developing a serious blood clot. The Sun didn’t list a source for its cow claim. 

The risk of being killed by a cow seems lower than this, but it is in the same ballpark as actually dying of one of these fatal clots after vaccination which, as said, is around one in a million. 

In September 2020 the Guardian quoted figures from the Health and Safety Executive (HSE), which monitors such incidents, showing that between March 2000 and March 2020, 98 people had been killed by cattle in the UK. 

Over roughly the same period (2000-2019) in the UK there were around 11.7 million deaths, meaning cows are responsible for around one in a million deaths. 

However, of the deaths recorded by the HSE, 22 were members of the public. The rest were either farmers or farm workers. So your likelihood of dying from a cow is much lower than your likelihood of dying from a blood clot after being vaccinated, if you’re not a farmer.

You’re far more likely to die in a car crash this year 

In the same Q&A section of the paper, The Sun also claimed a person is “far more likely” to die in a car crash this year than develop a serious blood clot from the AstraZeneca vaccine. It said the likelihood of this was one in 20,000. 

Again, The Sun doesn’t source this claim, but if you Google search ‘likelihood of death in car accident UK’, or similar search terms, it is the first number that appears in the results. 

This number appears on the online version of Bandolier, which describes itself as an “independent journal about evidence-based healthcare, written by Oxford scientists”. The most recent post on the site appears to be from 2010. 

A page on the site states: “While the risk of dying in a road accident in any year in the UK approaches 1 in 20,000, the lifetime risk is 1 in 240.”

According to the sources listed on the page, this figure has been calculated using Department of Transport data from 2004, now 17 years out of date. 

More recent data on road deaths in Great Britain is from the year ending June 2019, during which 1,870 fatalities were recorded. This number includes people in cars, pedestrians, motorcyclists, cyclists and ‘other’ road users. 

Using the ONS population estimate for mid-2019, the likelihood of dying in a road accident over the period of a single year across the entire population works out at approximately one in 35,720. One in 310 deaths in 2019 was a road death.

This means it is correct to say you are more likely to die in a crash this year than develop serious blood clots from the AstraZeneca vaccine.

Hard to quantify the risk of being hit in your home by a plane falling out of the sky 

In Thursday’s edition of its London Playbook newsletter, POLITICO quoted figures from the British Medical Journal (BMJ), which states that there’s a one in 250,000 chance of being hit in your home by a plane falling out of the sky. 

The BMJ lists its source for this figure as a book called Up to Your Armpits in Alligators? How to Sort Out What Risks are Worth Worrying About!, published by an academic at the Risk Communication and Environmental Institute, Gainesville, Florida in 1997. 

While listed by the BMJ as a reasonable way of explaining risk in a healthcare context, it’s likely that this figure from more than 20 years ago, calculated in the US, doesn’t represent  the risk to a UK citizen in 2021. 

According to data collated by the World Bank, the number of passengers carried via plane in a year almost tripled between 1997 and 2019, indicating a significant increase in the amount of air traffic worldwide. The UK is also a more densely populated country than the US, so it’s possible that a piece of aircraft debris over the UK would be more likely to hit a house than in the US. 

But then air travel is also safer than it was 20 years ago.

Full Fact could not find any information on the risk of being hit in your home by a plane falling from the sky, in the UK, in 2021.