Kermack-McKendrick type models for epidemics with nonlocal aggregation terms

TL;DR

This paper develops a well-posedness theory for nonlocal aggregation SIR epidemic models with spatial heterogeneity, analyzes steady states, and provides numerical simulations, advancing understanding of spatial epidemic dynamics with complex interactions.

Contribution

It introduces a novel nonlocal aggregation framework for SIR models, establishing existence, uniqueness, and stability results, and explores steady states with numerical validation.

Findings

Well-posedness of the nonlocal SIR model on  with smooth initial data.

Existence of non-trivial steady states under certain threshold conditions.

Numerical simulations illustrating the model's behavior and steady states.

Abstract

We propose an approach to model spatial heterogeneity in SIR-type models for the spread of epidemics via \emph{nonlocal aggregation terms}. More precisely, we first consider an SIR model with spatial movements driven by nonlocal aggregation terms, in which the inter-compartment and intra-compartment interaction terms are distinct, and modelled through smooth interaction kernels. For the Cauchy problem of said model we provide a full well-posedness theory on $\R^2$ for $L^1\cap L^\infty \cap H^1$ initial conditions. The existence part is achieved by considering an approximated model with artificial linear diffusion, for which existence and uniqueness is proven via Duhamel's principle and Banach fixed point, and by providing suitable uniform estimates on the approximated solution in order to pass to the limit via classical compactness techniques. To prove uniqueness, we use classical $L^2$-stability which relies on the $H^1$-regularity of the solution. In the second part of the paper we provide a brief, general discussion on the steady states for these type of models, and display a specific example of non-trivial steady states for an SIS model with aggregations (driven by a single repulsive-attractive potential), the existence of which is determined by a threshold condition for a suitable "space-dependent" basic reproduction rate. We complement the analysis with numerical simulations on the SIS model.