Risk assessments jab at our biases

I BELIEVE THE INVENTION OF COVID VACCINES, INCLUDING SOME SIGNIFICANT INPUT FROM OUR GEELONG CSIRO FACILITY, IS ONE OF THE GREATEST ACHIEVEMENTS OF THE 21ST CENTURY.”

HOW might we best decide whether and when to get a COVID vaccine shot? I’m certainly glad to have recently got the AstraZeneca shot. It’s a relief to feel much more protected from the greatest risks posed by the disease.

However, I understand from GP friends that many people are reluctant to get the jab, including older people with seemingly the most to gain. This partly relates to fear of developing life-threatening blood clots from the more widely available AstraZeneca vaccine.

However, the reported incidence of such blood clots is about four in a million, with about one in a million resulting in death.

This is a minuscule risk, especially when contrasted with risk estimates of approximately 500 in a million getting blood clots from the contraceptive pill, or over 150 in a million from long-haul flights. Why is there so much perceived risk from a widely used and effective COVID vaccine relative to other choices that involve about 50 to 100 times greater risk?

I think the answer relates to common thinking patterns known as cognitive biases, which can strongly influence our perception of risk. One is confirmation bias, whereby we selectively look for evidence that confirms a particular viewpoint, such as that the AZ vaccine can lead to blood clots.

This can combine with the salience bias, which invites us to pay more attention to outcomes that are more dramatic and subsequently lead us to have exaggerated estimates of their likelihood.

I believe media outlets promoted these biases by seeking out and quickly reporting on a couple of early cases involving fatal blood clots suspected of having a vaccine link, adding a dramatic news item to bulletins.

This is likely to have promoted a thinking bias called the “availability heuristic”, whereby we over-estimate the probability of events that we recall more easily, including recent dramatic events. We weren’t receiving more representative, but less dramatic or newsworthy, information in news bulletins such as days when there were no reported blood clots despite tens of thousands of vaccine shots being administered.

Some understandable cognitive biases could also impact on medical advice, including one related to regret. Research shows that doctors will typically experience a greater sense of responsibility and regret if they encouraged a particular active treatment that led to a negative outcome than if they were cautious and used a wait-and-see approach that might have led to a similarly negative outcome.

This can lead to exaggerated perception of risk of the active treatment, which is further strengthened if the negative outcome is more easily imagined, such as after dramatic media coverage.

An additional bias may relate to situations involving more than one treatment alternative as is the case with COVID vaccines. Research shows that when there’s an element of uncertainty over which treatment is best when more than one is available, it can lead to increased hesitancy to recommend either.

I believe the invention of COVID vaccines, including some significant input from our Geelong CSIRO facility, is one of the greatest achievements of the 21st century. We also have the great advantage of relatively little exposure to COVID relative to almost all other countries.

It is also our good fortune to have the capacity to manufacture the AZ vaccine onshore, through CSL. However, I fear that these uncommon local advantages, combined with the boon of the vaccines being developed earlier than predicted, are at risk of being offset by the initially slow voluntary uptake of the vaccine in Australia.

If so, this could partly be the result of exaggerated concerns about the vaccines, influenced at least in part by common and understandable cognitive biases. I think there is much to gain from greatly reducing the risk of severe disease and death as well as speeding up herd immunity with the help of vaccines. In my view, that would spell more security and freedom with typically minimal risk to the vast majority of us.

Naturally, for those with various health complications, there may be some extra reasons to be cautious and good reason to discuss the risks with your GP.

Even then, however, there’s value in taking these common cognitive biases into account lest they unduly sway our decisions.