Apollo's Arrow: The Profound and Enduring Impact of Coronavirus on the Way We Live

by Nicholas A. Christakis MD PhD

Consider the following simplified illustration of this idea. Say there is a group of one hundred people who are infected with a virus. One is a super-spreader who can spread disease to three hundred people, and ninety-nine are not infectious at all. The average R0 in this hypothetical population of one hundred is 3.0, but there is a very large variation in infectiousness. If just one person from such a population is chosen at random to travel to another place, that means that, ninety-nine out of a hundred times, there will be no epidemic as a result. By comparison, if there is a group of one hundred people who can each spread the disease to three people, the average R0 is still 3.0, but now there is no variation in infectiousness. Picking one member of this second group to travel to another place means that surely an epidemic will start there. Although in both groups the pathogen has the same average R0, the fact that the variation of the R0 is smaller for the latter group means that the germ is much more likely to seed new infections in other communities.