Universality classes in the time evolution of epidemic outbreaks on complex networks

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Main Authors: Samsel, Mateusz J., Fronczak, Agata, Fronczak, Piotr
Format: Preprint
Published: 2025
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author Samsel, Mateusz J.
Fronczak, Agata
Fronczak, Piotr
author_facet Samsel, Mateusz J.
Fronczak, Agata
Fronczak, Piotr
contents We investigate the full temporal evolution of epidemic outbreaks in complex networks, focusing on the susceptible-infected (SI) model of disease transmission. Combining theoretical analysis with large-scale numerical simulations, we uncover two universal patterns of epidemic growth, determined by the structure of the underlying network. In small-world networks, the prevalence follows a Gompertz-like curve, while in fractal networks it evolves according to Avrami-type dynamics, which is typical of spatially constrained systems. These regimes define distinct universality classes that remain robust across arbitrary transmission rates. Notably, our approach provides explicit analytical formulas for the global epidemic prevalence and class-specific scaling relations capturing its dependence on the transmission rate. We show that the commonly assumed early exponential growth occurs only in small-world networks, where it corresponds to the short-time approximation of the Gompertz function. In contrast, this exponential phase is entirely absent in fractal networks, where spreading is markedly slower and governed by different mechanisms. Our approach clarifies the structural origins of these contrasting behaviors and offer a unified framework for understanding epidemic dynamics across diverse network topologies.
format Preprint
id arxiv_https___arxiv_org_abs_2503_09167
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Universality classes in the time evolution of epidemic outbreaks on complex networks
Samsel, Mateusz J.
Fronczak, Agata
Fronczak, Piotr
Physics and Society
Disordered Systems and Neural Networks
Statistical Mechanics
We investigate the full temporal evolution of epidemic outbreaks in complex networks, focusing on the susceptible-infected (SI) model of disease transmission. Combining theoretical analysis with large-scale numerical simulations, we uncover two universal patterns of epidemic growth, determined by the structure of the underlying network. In small-world networks, the prevalence follows a Gompertz-like curve, while in fractal networks it evolves according to Avrami-type dynamics, which is typical of spatially constrained systems. These regimes define distinct universality classes that remain robust across arbitrary transmission rates. Notably, our approach provides explicit analytical formulas for the global epidemic prevalence and class-specific scaling relations capturing its dependence on the transmission rate. We show that the commonly assumed early exponential growth occurs only in small-world networks, where it corresponds to the short-time approximation of the Gompertz function. In contrast, this exponential phase is entirely absent in fractal networks, where spreading is markedly slower and governed by different mechanisms. Our approach clarifies the structural origins of these contrasting behaviors and offer a unified framework for understanding epidemic dynamics across diverse network topologies.
title Universality classes in the time evolution of epidemic outbreaks on complex networks
topic Physics and Society
Disordered Systems and Neural Networks
Statistical Mechanics
url https://arxiv.org/abs/2503.09167