Spatial Heterogeneity Can Lead to Substantial Local Variations in COVID-19 Timing and Severity

TL;DR

This study shows that spatial heterogeneity significantly influences local COVID-19 outbreak timing and severity, leading to disparities in healthcare demand and individual risk perception, even when overall epidemic patterns appear uniform.

Contribution

It introduces geographically detailed diffusion models based on spatial features of interpersonal networks, revealing complex local variations in COVID-19 spread not captured by traditional models.

Findings

Heterogeneity causes large local variations in outbreak timing and severity.

Local outbreaks can lag behind the overall epidemic curve.

Spatial network structure leads to highly non-uniform diffusion behavior.

Abstract

Standard epidemiological models for COVID-19 employ variants of compartment (SIR) models at local scales, implicitly assuming spatially uniform local mixing. Here, we examine the effect of employing more geographically detailed diffusion models based on known spatial features of interpersonal networks, most particularly the presence of a long-tailed but monotone decline in the probability of interaction with distance, on disease diffusion. Based on simulations of unrestricted COVID-19 diffusion in 19 U.S cities, we conclude that heterogeneity in population distribution can have large impacts on local pandemic timing and severity, even when aggregate behavior at larger scales mirrors a classic SIR-like pattern. Impacts observed include severe local outbreaks with long lag time relative to the aggregate infection curve, and the presence of numerous areas whose disease trajectories correlate poorly with those of neighboring areas. A simple catchment model for hospital demand illustrates potential implications for health care utilization, with substantial disparities in the timing and extremity of impacts even without distancing interventions. Likewise, analysis of social exposure to others who are morbid or deceased shows considerable variation in how the epidemic can appear to individuals on the ground, potentially affecting risk assessment and compliance with mitigation measures. These results demonstrate the potential for spatial network structure to generate highly non-uniform diffusion behavior even at the scale of cities, and suggest the importance of incorporating such structure when designing models to inform healthcare planning, predict community outcomes, or identify potential disparities.