And so the epidemic encourages us to think of ourselves as belonging to a collective. It pushes us to behave in a way that is unthinkable under normal circumstances, to recognize that we are inextricably connected to other people, to consider their existence and well-being in our individual choices. In the contagion we rediscover ourselves as part

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Epidemics are mathematical emergencies first and foremost. Because math isn’t the science of numbers – not really – it’s the science of relations: it describes the bonds and the exchanges between different entities, regardless of what these entities might be made of, abstracting them into letters, functions, vectors, points, and planes. The contagi

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In theory, any disease with an R0 greater than 1 will eventually spread to the entire population in the absence of vaccines or quarantines. But the numbers are sometimes much higher than this: R0 was about 3 for the Spanish flu, 6 for smallpox, and 15 for measles. It is perhaps well into the triple digits for malaria, one of the deadliest diseases

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Contact tracing—the gumshoe work of the public health system whereby one goes backward from a known case to see who the patient has been in contact with—revealed that at least sixty people had been exposed to Patient Zero. Amazingly, none of them got sick. Later genetic analyses confirmed that this patient was very likely not responsible for the ep

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