The Rules of Contagion
First published in Great Britain in 2020 by
Profile Books Ltd
29 Cloth Fair
London
EC1A 7JQ
www.profilebooks.com
Copyright © Adam Kucharski, 2020
The moral right of the author has been asserted.
All rights reserved. Without limiting the rights under copyright reserved above, no part of this publication may be reproduced, stored or introduced into a retrieval system, or transmitted, in any form or by any means (electronic, mechanical, photocopying, recording or otherwise), without the prior written permission of both the copyright owner and the publisher of this book.
A CIP catalogue record for this book is available from the British Library.
ISBN 9781788160193
eISBN 9781782834304
Contents
Cover
Adam Kucharski
Dedication
The Rules of Contagion
Introduction
1. A theory of happenings
2. Panics and pandemics
3. The measure of friendship
4. Something in the air
5. Going viral
6. How to own the internet
7. Tracking outbreaks
8. A spot of trouble
Notes
Further reading
Acknowledgements
Adam Kucharski is an associate professor at the London School of Hygiene & Tropical Medicine. A mathematician by training, his work on global outbreaks such as the Ebola epidemic and the Zika virus has taken him from villages in the Pacific Islands to hospitals in Latin America. He is a TED fellow and winner of the 2016 Rosalind Franklin Award Lecture and the 2012 Wellcome Trust Science Writing Prize. The author of The Perfect Bet, his writing has appeared in the Observer, Financial Times, Scientific American and New Statesman.
Also by Adam Kucharski
The Perfect Bet
For Emily
The Rules of Contagion
Why Things Spread — and Why They Stop
Adam Kucharski
Introduction
A few years ago, I accidentally caused a small outbreak of misinformation. On my commute to work, a friend who works in tech had sent me a stock photo of a group hunched over a table wearing balaclavas. We had a running joke about how news articles on computer hacking would often include staged pictures of people looking sinister. But this photo, below a headline about illicit online markets, had taken things much further: as well as balaclavas, there was a pile of drugs, and a man who apparently wasn’t wearing any trousers. It seemed so surreal, so inexplicable.
I decided to tweet it. ‘This stock photo is fascinating in so many ways,’ I wrote,[1] pointing out all the quirks in the image. Twitter users seemed to agree, and within minutes dozens of people had shared and liked my post, including several journalists. Then, just as I was starting to wonder how far it might spread, some users pointed out that I’d made a mistake. It wasn’t a stock photo at all; it was a still image from a documentary about drug dealing on social media. Which, in retrospect, made a lot more sense (apart from the lack of trousers).
Somewhat embarrassed, I posted a correction, and interest soon faded. But even in that short space of time, almost fifty thousand people had seen my tweet. Given that my job involves analysing disease outbreaks, I was curious about what had just happened. Why did my tweet spread so quickly at first? Did that correction really slow it down? What if people had taken longer to spot the mistake?
Questions like these crop up in a whole range of fields. When we think of contagion, we tend to think about things like infectious diseases or viral online content. But outbreaks can come in many forms. They might involve things that bring harm – like malware, violence or financial crises – or benefits, like innovations and culture. Some will start with tangible infections such as biological pathogens and computer viruses, others with abstract ideas and beliefs. Outbreaks will sometimes rise quickly; on other occasions they will take a while to grow. Some will create unexpected patterns and, as we wait to see what happens next, these patterns will fuel excitement, curiosity, or even fear. So why do outbreaks take off – and decline – in the way they do?
Three and a half years into the First World War, a new threat to life appeared. While the German army was launching its Spring Offensive in France, across the Atlantic people had started dying at Camp Funston, a busy military base in Kansas. The cause was a new type of influenza virus, which had potentially jumped from animals into humans at a nearby farm. During 1918 and 1919, the infection would become a global epidemic – otherwise known as a pandemic – and would kill over fifty million people. The final death toll was twice as many as the entire First World War.[2]
Over the following century, there would be four more flu pandemics. This raises the obvious question: what will the next one look like? Unfortunately it’s difficult to say, because previous flu pandemics were all slightly different. There were different strains of the virus, and outbreaks hit some places harder than others. In fact, there’s a saying in my field: ‘if you’ve seen one pandemic, you’ve seen … one pandemic.’[3]
We face the same problem whether we’re studying the spread of a disease, an online trend, or something else; one outbreak won’t necessarily look like another. What we need is a way to separate features that are specific to a particular outbreak from the underlying principles that drive contagion. A way to look beyond simplistic explanations, and uncover what is really behind the outbreak patterns we observe.
That’s the aim of this book. By exploring contagion across different areas of life, we’ll find out what makes things spread and why outbreaks look like they do. Along the way, we’ll see the connections that are emerging between seemingly unrelated problems: from banking crises, gun violence and fake news to disease evolution, opioid addiction and social inequality. As well as covering the ideas that can help us to tackle outbreaks, we’ll look at the unusual situations that are changing how we think about patterns of infections, beliefs, and
