Impact of behavioral heterogeneity on epidemic outcome and its mapping into effective network topologies

TL;DR

This paper introduces a minimal extended SIR model, HeSIR, capturing behavioral heterogeneity and homophily effects, deriving epidemic thresholds, and mapping the dynamics onto modified networks to better understand epidemic outcomes.

Contribution

It presents the HeSIR model incorporating behavioral heterogeneity, derives analytical epidemic thresholds, and links epidemic dynamics to network structure, advancing understanding of behavioral impacts on epidemics.

Findings

Heterogeneity and homophily significantly influence epidemic thresholds.

A resurgence regime can occur just beyond the classical epidemic threshold.

The HeSIR model maps onto a standard SIR process on a modified network.

Abstract

Human behavior plays a critical role in shaping epidemic trajectories. During health crises, people respond in diverse ways in terms of self-protection and adherence to recommended measures, largely reflecting differences in how individuals assess risk. This behavioral variability induces effective heterogeneity into key epidemic parameters, such as infectivity and susceptibility. We introduce a minimal extension of the susceptible-infected-removed~(SIR) model, denoted HeSIR, that captures these effects through a simple bimodal scheme, where individuals may have higher or lower transmission--related traits. We derive a closed-form expression for the epidemic threshold in terms of the model parameters, and the network's degree distribution and homophily, defined as the tendency of like--risk individuals to preferentially interact. We identify a resurgence regime just beyond the classical threshold, where the number of infected individuals may initially decline before surging into large-scale transmission. Through simulations on homogeneous and heterogeneous network topologies we corroborate the analytical results and highlight how variations in susceptibility and infectivity influence the epidemic dynamics. We further show that, under suitable assumptions, the HeSIR model maps onto a standard SIR process on an appropriately modified contact network, providing a unified interpretation in terms of structural connectivity. Our findings quantify the effect of heterogeneous behavioral responses, especially in the presence of homophily, and caution against underestimating epidemic potential in fragmented populations, which may undermine timely containment efforts. The results also extend to heterogeneity arising from biological or other non-behavioral sources.