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14 April 2021updated 06 Sep 2021 2:33pm

There’s an evolutionary explanation for our irrational fears over vaccines

Injecting a mysterious substance into the body feels unsettling, and this feeling can’t be effectively countered with smug, technocratic messaging.

By Louise Perry

I am the proud owner of a book titled Dogs Bite: But Balloons and Slippers are More Dangerous, written by an American animal behaviourist called Janis Bradley. I bought it partly for superficial reasons: I liked the title, and I also liked the picture on the cover of an endearing mongrel chewing a slipper. But it turned out to be a truly excellent purchase, since this is a book that provides a timely insight into why we find some risks so much more frightening than others. 

Bradley points out that humans of all ages are very, very unlikely to be seriously hurt by a dog, let alone killed by one. Dogs are less dangerous than kitchen utensils, drapery cords, five-gallon water buckets, swimming pools, skateboards and bikes. And they are a lot less dangerous than guns, cars and other people. 

One particularly memorable graph in Dogs Bite shows some of the causes of fatal injuries in children, with dogs on average causing ten deaths a year in the US, coming in behind both balloons (11 deaths) and playground equipment (15 deaths). In contrast, the number of child deaths caused by human caregivers averages 826 annually. And given that children who live with pets are less likely to develop potentially life-threatening allergies, it is probably safer, on balance, for risk-averse parents to choose having a dog over not having one. 

Bradley also estimates that you are roughly five times more likely to be killed by a bolt of lightning than by a dog. This particular statistic caught my eye because it reminded me of an observation made by a team of scientists from the universities of Oxford and Cambridge in June last year: that UK children under the age of 15 are more likely to be hit by lightning than to die from Covid-19. 

A lightning strike is the archetypal rare event, and although there are safeguards in place to protect the public – such as modern building regulations, which have successfully reduced lightning deaths – it is not a risk that most of us spend much time contemplating. In contrast, fear of flying is a common phobia, even though the risk of being in a plane crash is lower than the risk of being struck by lightning. In fact, air travel is by some measures the safest mode of transportation, and yet knowing this does absolutely nothing to cure my mild aversion to flying. No matter how much data I read, I still don’t like being trapped in a metal box, miles above the ground. 

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Our brains are bad at assessing risk, particularly risks that are novel in evolutionary terms. The ongoing controversy over the association between the AstraZeneca vaccine and the incidence of blood clots reveals the inherent difficulty humans have in making decisions in relation to risks that are very small, but also very frightening. 

In the UK, blood clots have occurred in people receiving the AstraZeneca vaccine at a rate of roughly one in every 250,000 – a risk level that has caused sufficient alarm to halt the vaccine roll-out in some countries. These blood clots seem to occur more often in young people, who are also very unlikely to die from coronavirus and are thus potentially tasked with choosing between exposing themselves to either a not-very-dangerous disease or its not-very-dangerous cure. 

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For comparison, about 1 in 1,000 women per year who are taking birth control pills will develop a blood clot. Some health experts have sought to reassure the public of the safety of the AstraZeneca jab by pointing out that it is significantly less dangerous than the pill, which is taken every day by millions of UK women. 

This argument is rather less reassuring to women who are concerned about whether taking the pill might increase the risk the AstraZeneca vaccine poses to them, and to those who are rightfully aggrieved that the side effects of hormonal contraception are still poorly understood and can very occasionally prove lethal.

Personally, seeing this comparison repeatedly made in the media over the past fortnight has not made me any more eager to accept the vaccine. It has, however, made me a little more reluctant to go back on hormonal birth control – and this was not, I think, what the public health messaging was aiming for.

I don’t think this is an uncommon failing on my part. Our irrational fears are the result not of stupidity but rather of evolution. As Janis Bradley so rightly observes in Dogs Bite, although humans have lived alongside domesticated dogs for more than 10,000 years, that still represents only a small fraction of our species’ history, meaning it doesn’t take much to persuade our limbic brains to fear wolfish animals with big teeth. 

The popularity of the anti-vax movement suggests vaccines are one of those things – like flying or dog bites – that provoke an outsized fear response, despite all the data demonstrating their safety. For many people, there is something about injecting a mysterious substance into the body that feels unsettling, and this feeling can’t be effectively countered with a smug, technocratic message, bombarding the public with very large or very small numbers and then demonising those who remain unpersuaded. 

Calling Brexit voters idiots didn’t stop us from leaving the EU, and nor is this strategy likely to increase the rates of vaccine uptake. It is very hard to intuitively engage with the difference between a risk of one in 10,000, or one in a million, or one in a billion – if you’re asking the public to count the zeros, you’ve lost the emotional message.