Microscopic dynamics of contagion using active Brownian particles: universal scaling and propagation controlled by protection
Abstract
Understanding how individual protection and population density influence epidemic spreading remains a central challenge in epidemiology. While classical compartmental models successfully describe the temporal evolution of epidemics, they do not explicitly account for the microscopic motion and spatial organisation of individuals. Here, we investigate contagion dynamics using an agent-based model of Active Brownian Particles (ABPs), where self-propelled agents interact through local contact and a prescribed fraction of the population is protected. By systematically varying the protected-agent fraction and the population density, we identify two distinct contagion regimes separated by a crossover protection of approximately 30%. Below this threshold, the maximum contagion rate follows the universal scaling νmax∝ϕ1/2, indicating that disease transmission is governed primarily by frequency of encounters. Above the threshold, universal scaling is lost and protection becomes the dominant mechanism controlling epidemic spreading, with the strongest suppression occurring in low-density populations. These results demonstrate that microscopic active-matter models provide a powerful framework for investigating epidemic dynamics beyond the assumptions of well-mixed population models and reveal how spatial organisation and individual protection jointly determine contagion dynamics.
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BibTeX
@misc{regaladoalvarado2026microscopic,
title = {{Microscopic dynamics of contagion using active Brownian particles: universal scaling and propagation controlled by protection}},
author = {Isela Sicarú Regalado-Alvarado and Francisco Alarcón},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.01927},
eprint = {2609.01927},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.01927},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - UNPB
TI - Microscopic dynamics of contagion using active Brownian particles: universal scaling and propagation controlled by protection
AU - Isela Sicarú Regalado-Alvarado
AU - Francisco Alarcón
PY - 2026
DA - 2026/09/01
PB - arXiv
DO - 10.48550/arxiv.2609.01927
UR - https://arxiv.org/abs/2609.01927
AB - Understanding how individual protection and population density influence epidemic spreading remains a central challenge in epidemiology. While classical compartmental models successfully describe the temporal evolution of epidemics, they do not explicitly account for the microscopic motion and spatial organisation of individuals. Here, we investigate contagion dynamics using an agent-based model of Active Brownian Particles (ABPs), where self-propelled agents interact through local contact and a prescribed fraction of the population is protected. By systematically varying the protected-agent fraction and the population density, we identify two distinct contagion regimes separated by a crossover protection of approximately 30%. Below this threshold, the maximum contagion rate follows the universal scaling ν_max∝ϕ^1/2, indicating that disease transmission is governed primarily by frequency of encounters. Above the threshold, universal scaling is lost and protection becomes the dominant mechanism controlling epidemic spreading, with the strongest suppression occurring in low-density populations. These results demonstrate that microscopic active-matter models provide a powerful framework for investigating epidemic dynamics beyond the assumptions of well-mixed population models and reveal how spatial organisation and individual protection jointly determine contagion dynamics.
ER -