An asteroid big enough to kill a city full of people hits the Earth about once every 1,000 years. Most people would agree that their risk of being hit by an asteroid is so low that there are more important things to worry about.
But what about a flu pandemic? It’s a difficult call. History suggests we can expect another global pandemic, yet it is devilishly hard to predict when. On the other hand, if one did strike its impact would be immense.
So how does a government respond to a low-risk, high-impact scenario? It may seem obvious that drugs and vaccines should be stockpiled and plans put in place to cope with an outbreak. But which drugs and which vaccines? Such stocks are expensive and somebody has to do all that planning. Is it a good use of time and money when there are so many other priorities? What about other possible challenges: XDR-TB (extensively drug-resistant tuberculosis); antibiotic-resistant bacteria; and gonorrhoea and other sexually transmitted infections?
Governments seek advice, including from scientists, and tools such as modelling can provide useful input. Yet knowledge will be incomplete and evidence disputed. Other factors will also influence decisions – such as a government’s political philosophy, economic circumstances and pressure from the media.
Individuals will face different issues. Sales of chicken plummeted when avian flu was discovered in Norfolk, while uptake of the MMR (measles, mumps and rubella) vaccine dropped when fears of a link with autism were raised. It is tempting to call such responses irrational, given the extremely low risks involved. (In the case of MMR, the link to autism has now been thoroughly disproven.)
But people are simply weighing up what they perceive to be the risks and benefits. Why take even a small (or perceived) risk if it can be easily avoided with no apparent consequences? A greater risk will be tolerated if there is a corresponding trade-off in benefits – for instance, the possibility of mobile phones being harmful is more than outweighed by their value to us.
In terms of emerging infections our behaviour will depend on our perceptions (Is the threat real?) and the extent to which proposed measures inconvenience us (What will I have to give up?), and, of course, our individual personalities. Voluntarily avoiding chicken for a few weeks ‘just in case’ is very different from not being allowed to leave the house