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9 April 2021

What AstraZeneca vaccine fears reveal about our skewed sense of risk

No one gives a second thought to the dangers of driving to a vaccination centre, yet that is a far more significant risk than blood clots.

By Phil Whitaker

In the early weeks of the Covid-19 immunisation campaign, most of our deliveries were of the American-developed Pfizer vaccine. Only one person actually refused to have it, but typically three or four patients during every session would express concern when I was obtaining their consent.

Their anxieties centred around two things. The Pfizer jab had got off to a disastrous start: it caused two cases of anaphylaxis (life-threatening allergic reactions) on pretty much its first day of use in the UK, which made headline news. As a result, all patients were being required to stay under observation for 15 minutes after injection.

And the Pfizer was also a palpably new technology, requiring ultra-low temperature storage and extremely careful handling – nothing like any vaccine ever used before. Again and again, spooked patients expressed disappointment that I didn’t have the Oxford-AstraZeneca (OAZ) vaccine to give them instead. Needing only fridge-temperature storage, it felt much more familiar to them, just like the flu jabs rolled out every year. And there was that reassuring connection with an august British academic institution to boot.

The mood started to shift several weeks ago. Adjustments to the consent process, which screened out patients with histories of serious allergic reactions, have prevented further instances of anaphylaxis with the Pfizer; those initial cases have faded in the collective memory. And a drip feed of stories about the OAZ from other countries – first questioning its efficacy in older age groups; latterly restricting its use in younger patients over a possible link with a rare type of blood clot – have somewhat tarnished its reputation. In recent OAZ vaccination sessions, I’ve typically had three or four patients expressing disappointment that I haven’t got the Pfizer jab to give them instead.

This flux in public confidence in the two vaccines illustrates much about how we perceive risk. We are confident and comfortable with things that feel familiar, whereas the unusual or the alien generate instinctive wariness. And we are hugely swayed by stories. When our media is saturated with coverage of one adverse outcome or another, it magnifies the risk disproportionately in our minds.

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[see also: Something was missing from the government’s announcement on AstraZeneca]

Our notions of risk are also heightened when crystallised by making a decision. We may be aware of the dangers of Covid infection – immeasurably more likely to kill or disable patients than any vaccine side effect – yet we are never faced with a choice over whether or not we catch it. It feels like a chance possibility, one that may never come to pass. But presenting an arm to a needle-wielding vaccinator is a conscious act, and our risk-assessing processes are set aflame when we have to decide whether to roll up our sleeve. Are we about to do something entirely deliberately that just might cause us harm?

There are no medical interventions without risk. All drugs have the potential to cause side effects, from humble paracetamol through to the most aggressive chemotherapy. Many of them are at the level of nuisance – symptoms such as diarrhoea or headache – but serious events very occasionally occur after pretty much any treatment. Any adverse outcome is a tragedy to the individual involved, and to their family and friends.

Yet so many other patients would be deprived of benefit were they put off undertaking a treatment over fears of rare disasters. How, then, to try to bring an appropriate perspective to our sense of risk?

The approach being taken by the Joint Committee on Vaccination and Immunisation (JCVI) is to weigh the potential harm from either having or not having the OAZ jab. Covid causes serious disease in around 4 per cent of patients, and death in around 0.5 per cent. Around a quarter of hospitalised Covid patients develop blood clots provoked by the infection. Currently, in every age group above 30 years old, the chance of a serious adverse outcome from Covid infection far outweighs any risk from OAZ vaccination.

For patients younger than 30, who are at low risk of developing severe Covid, the scales tip slightly the other way, hence the JCVI proposal to allow a choice of alternative vaccine products among this cohort. Yet once the inevitable third wave gets under way, and the chance of people contracting Covid increases again, this balance will shift, and OAZ vaccination will be safer than the virus even in the youngest adults.

A different approach is to relate the potential harms to everyday activities we all take for granted. The risk of developing the rare type of blood clot being linked to the OAZ vaccine is around one in 250,000; the risk of dying as a result is around one in a million. The annual risk of a fatal road traffic accident in the UK approaches one in 20,000 – car travel is 50 times more dangerous than being immunised with the OAZ jab.

No one gives a second thought to the potential dangers of driving to a mass vaccination centre, yet arguably that is the more significant risk we’d be taking in seeking protection from contracting Covid-19.

[see also: Why is the UK offering under-30s an alternative to the AstraZeneca vaccine?]