# Asymmetric percolation drives a double transition in sexual contact networks

## TL;DR

This study models how asymmetric infectious periods between males and females in sexual contact networks cause two epidemic transitions, revealing a hidden core-periphery structure and implications for Zika virus surveillance.

## Contribution

It introduces an exact analytical model of asymmetric percolation on sexual contact networks, uncovering a double transition and a hidden core-periphery structure caused by infectiousness asymmetry.

## Key findings

- Two epidemic transitions due to asymmetric percolation
- Emergence of a core-periphery structure in the network
- Potential bias in ZIKV surveillance and testing

## Abstract

Zika virus (ZIKV) exhibits unique transmission dynamics in that it is concurrently spread by a mosquito vector and through sexual contact. We show that this sexual component of ZIKV transmission induces novel processes on networks through the highly asymmetric durations of infectiousness between males and females -- it is estimated that males are infectious for periods up to ten times longer than females -- leading to an asymmetric percolation process on the network of sexual contacts. We exactly solve the properties of this asymmetric percolation on random sexual contact networks and show that this process exhibits two epidemic transitions corresponding to a core-periphery structure. This structure is not present in the underlying contact networks, which are not distinguishable from random networks, and emerges because of the asymmetric percolation. We provide an exact analytical description of this double transition and discuss the implications of our results in the context of ZIKV epidemics. Most importantly, our study suggests a bias in our current ZIKV surveillance as the community most at risk is also one of the least likely to get tested.