For centuries mankind has waged war against the infections that, left untreated, would have the power to wipe out communities, or even entire populations. Yet for all our advanced scientific knowledge, only one human disease – smallpox – has ever been eradicated globally. In recent years, outbreaks of Ebola and Zika have provided vivid examples of how difficult it is to contain an infection once it strikes, and the panic that a rapidly spreading epidemic can ignite.