Whether it is disease epidemics or crime and terrorism, mathematical models can help countries plot outcomes and allocate resources. But models are just that, writes Kucharski: reality is messy and complex. If you build a model train set — no matter how skilful and full of add-ons such as delays, leaves on the line, faulty signals — it will always differ from reality in some way. There was some post-9/11 research into threats from bioterrorist attacks, which put possible fatalities at 77 trillion. Not bad for a world population of seven billion. The word coronavirus doesn’t crop up in this brilliant, dense, scholarly book. But Kucharski has pulled off the extraordinary trick of shining the brightest light, for this reader anyway, on this unseen, menacing, but ultimately beatable, enemy.

Kucharski, though, has made an extremely respectable stab at something broader, producing a work of contemporary relevance that Malcolm Gladwell devotees would enjoy: a blend of biology, mathematics, history, behavioural science and anecdote that reveals how diseases, ideas and behaviours are transmitted. His nicely observed analysis deserves to catch on. 

This is a hell of a moment for a book like this to come out, and some might assume it’s a lightning-fast cash-in on a global tragedy. They would be wrong. Coronavirus hadn’t even appeared when Kucharski delivered the manuscript, so the disease isn’t directly addressed here. But the principles of contagion, which, he argues, can be applied to everything from folk stories and financial crises to itching and loneliness, are suddenly of pressing interest to all of us. Kucharski, a mathematician who has worked on the fight against the ebola and zika viruses, believes that to master the diseases we first have to master the arithmetic.

I imagine that, in the publisher’s offices, they are having guilty celebrations that the book is coming out in the middle of the coronavirus outbreak: it is hard to imagine a more timely publication. And it is a useful, eye-opening read on that front, although it was written before the coronavirus was heard of. Unchecked, a disease with an R greater than one will form an S-shaped curve on a chart: the number of new infections shooting up, until it starts to run out of susceptible people. That still seems to be happening in China. It will also help you to understand the idea of “super-spreaders” and their role in keeping even quite low-R infections moving. One unlucky Briton apparently spread coronavirus to 11 people and has been termed a super-spreader.

The mathematics of contagion varies little from coronavirus to computer virus, financial risk to fake news. Now, with perfect timing, a good guide has arrived to pull together scientific knowledge about the way things spread and how to block (or encourage) their transmission. Adam Kucharski, an epidemiologist at the London School of Hygiene and Tropical Medicine, completed The Rules of Contagion before the novel coronavirus disease Covid-19 emerged in Wuhan — and he sensibly resisted rushing into a last-minute update or revision to take account of the new epidemic, which is developing so fast that anything he wrote about it would have been out of date before publication.