A Mathematician’s Guide to How Contagion Spreads

Adam Kucharski didn’t expect to publish a book about contagion in the middle of a global pandemic. But consider him less surprised than the rest of us. “In my field we always have the next pandemic on the radar,” he says. Kucharski, an epidemiologist at the London School of Hygiene and Tropical Medicine, is a mathematician by training. He uses data and models to predict how disease outbreaks will progress. His new book, The Rules of Contagion: Why Things Spread—and Why They Stop, lays out those tools and how they can be applied to other parts of life. Think methods to predict how panic might course through the global financial system, or how bad information is transmitted on Facebook. But most important, Kucharski says, is what he calls “epidemiological thinking.” That’s a mindset for dealing with incomplete information, as infectious-disease researchers must when they encounter a novel, fast-moving pathogen. Sometimes you might make bad assumptions, and your models might make predictions that never come to pass. But in a crisis, coming up with a hypothesis, even if it’s a rough one, is often the only way to get people to act.

Courtesy of Hachette Book Group
Kucharski spoke to WIRED from London, where he lives. This interview has been edited for length and clarity.WIRED: I want to ask about something you tweeted just a few minutes ago. It was an excerpt from a book by the British geographer Richard Burton about mosquitoes and malaria. Could you describe what he wrote and why it left an impression?Adam Kucharski: In the book I dig into the history of many principles of transmission, and one thing that struck me was this quote by a British geographer in the 1850s. Burton noted that in Somalia local people were drawing a link between the rise of mosquitoes in a given season and these fevers, which were probably malarial fevers. And he was very dismissive. He called it superstition. At the time, a lot of the thinking around malaria, certainly in the West, was one of “bad air.” The word malaria comes from mala aria—Italian for bad air. And it was very interesting to see that there were cultures in the world that hit on this other link. But it would take decades for the supposedly “enlightened” Western scientists to reach that same connection. It really does illustrate with some of these ideas that history is more complex than perhaps we think. In many cases, the credit is given very prominently to certain individuals without acknowledging some of the deeper origins.
WIRED: It’s not a perfect analogy, but when I read that, I couldn't help but think about the relearning of facts and evidence that’s happening right now with Covid-19. Other countries had learned a lot from diseases like SARS. Wuhan had months to learn about this virus before it spread widely in the US and Europe. Now we’re here rediscovering the effectiveness of things like masks.

AK: I think that's a very important point. Learning from what other countries are doing and not making the same mistakes again is crucial. It was quite striking how a lot of the discourse around the Ebola outbreaks, for example, was at times quite patronizing. People were saying, ‘We know how to control this. We know what measures work, so why aren't people doing them? Why aren't people just doing what they should be doing to reduce transmission?’ And of course, we've now got major epidemics in a number of countries that supposedly had high levels of preparedness. But transmission is not going down, because people aren't following those supposedly obvious things that can help reduce transmission. So I think it shows that the challenges are far more fundamental than we think they are, and we have to look widely for solutions to a problem this great. It's not the case that one group or one country is going to have the answers.