Epidemics, disorder, and percolation

TL;DR

This paper explores how disorder in contact strengths affects epidemic spread, showing that it broadens the percolation threshold and can lead to epidemic outbreaks even in networks with zero percolation threshold.

Contribution

It highlights the impact of contact strength disorder on epidemic percolation thresholds and provides examples of networks where this effect is significant.

Findings

Disorder broadens the epidemic percolation threshold.

In some networks, disorder causes the percolation threshold to be zero.

Geographical networks may not have zero percolation threshold despite disorder.

Abstract

Spatial models for spread of an epidemic may be mapped onto bond percolation. We point out that with disorder in the strength of contacts between individuals patchiness in the spread of the epidemic is very likely, and the criterion for epidemic outbreak depends strongly on the disorder because the critical region of the corresponding percolation model is broadened. In some networks the percolation threshold is zero if another kind of disorder is present, namely divergent fluctuations in the number of contacts. We give an example, a network with a well defined geography, where this is not necessarily so, and discuss whether real infection networks are likely to have this property.