What is the acceptable level of risk for Covid-19?

During the current coronavirus lockdown there had been a dramatic reduction in road traffic and hence, presumably, a dramatic reduction in casualties from road traffic accidents – something that is highly desirable.

Why did this have to wait for coronavirus? We could have instituted a national lockdown at any time in order to reduce road traffic accidents – but we didn’t. Why not? – because there is such a massive imbalance between the cost of a national lockdown and the benefit of reducing road traffic accidents.

The reality is that we tolerate about 1,700 deaths per year on the roads, not because it’s impossible to reduce the number but because the cost of reducing it is too high. In effect, there is an acceptable level of risk for road traffic casualties that we are willing to live with.

The same trade-off between the level of risk and the cost of risk reduction applies in many other situations. Society somehow find an acceptable equilibrium and life goes on (for most of us). How is the equilibrium arrived at?

Two crucial factors are diminishing returns and opportunity costs. It’s impossible to reduce most risks to zero regardless of the resources that are poured in, and the closer you get to zero the more resources are needed for the next increment of risk reduction. Because of diminishing returns there comes a point where it doesn’t make sense to go on. Furthermore, the resources devoted to reducing one risk cannot be devoted to reducing another: the lack of resources for reducing risk B is called an opportunity cost of reducing risk A. When the benefits of risk reduction are less than the opportunity costs (ie. the resources would be more effective for risk B than risk A), it’s time to stop.

Logically, the equilibrium levels of risk for the various hazards we face would themselves be perfectly balanced, so no benefit would be gained by transferring risk-reduction effort from one risk to another. But of course that doesn’t happen. Some risks are overlooked and starved of resources, while others are attention-grabbing and gain disproportionate resources.

Covid-19 is certainty attention-grabbing and there has been an astonishing investment in reducing its risk – a significant fraction of the UK’s and the world’s GDP. When this crisis investment is rolled back the virus won’t have disappeared. In order for life to return to something like normal in the exit phase and beyond, we will have to find an acceptable level of risk for Covid-19, which will not be zero.

The equilibrium will emerge in a mysterious way from the interaction of top-down guidance from experts and government, media interpretation/misinterpretation, and the bottom-up actions of individuals. We know in advance that the equilibrium will be illogical and full of anomalies – but it’s worth making every effort to reduce the illogicality and minimise the anomalies.

Although top-down guidance on Covid-19 has to be broad-brush, each individual has specific characteristics that determine their personal vulnerability. We need top-down guidance to be matched by advice for each individual, explaining appropriate behaviours to manage their personal Covid-19 risk.

This could be provided by a system (on-line or paper-based) that receives data about relevant characteristics of an individual, and responds with recommendations that are consistent with top-down guidance but customised for the individual; all at a suitable level of detail. Easier said than done! – but worth trying.

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