Outbreak dynamics and population vulnerability in stochastic epidemic models on networks

TL;DR

This paper investigates how network structure, subpopulation sizes, and immunity influence outbreak sizes and vulnerability in stochastic epidemic models, revealing counterintuitive effects of immunity distribution on epidemic control.

Contribution

It provides new analytical and simulation insights into how network architecture and immunity distribution affect epidemic dynamics and vulnerability.

Findings

Networked populations often have lower mean outbreak sizes than homogeneous populations.

Small amounts of random prior immunity can significantly reduce outbreak sizes in networks.

Networked populations remain vulnerable to subsequent outbreaks even after initial outbreaks end.

Abstract

During infectious disease epidemics, pathogen transmission occurs in host populations made up of interacting subpopulations. Using stochastic simulation and analytical approximations, we examine how outbreak sizes in networked populations depend on network architecture, subpopulation sizes and the strength of coupling between subpopulations. We find, as expected, that mean outbreak sizes are frequently lower in networked populations than in homogeneous populations with the same basic reproduction number. However, after an outbreak ends, a networked population is often vulnerable to further outbreaks, and the ending of an outbreak may not imply herd immunity in any sense. Another key finding is that a relatively small amount of randomly distributed prior immunity can be more protective in a networked population than a homogeneous population, a phenomenon which can be reproduced analytically in certain cases. We also find that in networked populations, randomly distributed prior immunity is often more protective than infection-acquired immunity; but this conclusion can be reversed in populations with highly variable susceptibility. All of these conclusions have implications for designing outbreak control strategies that aim to reduce pathogen transmission during epidemics.