Mobility and the spatial spread of SARS-CoV-2 in Belgium

TL;DR

This study analyzes mobility and COVID-19 data across Belgian regions, revealing that movement patterns significantly influenced early viral spread and excess mortality, with correlations weakening as the epidemic progressed.

Contribution

It introduces a detailed analysis of mobility's impact on SARS-CoV-2 spread in Belgium using innovative connectivity and time series comparison methods.

Findings

Mobility decreased during high-incidence periods.

Arrondissements show different epidemic progression patterns.

Connectivity with initial outbreak areas correlates with excess mortality.

Abstract

We analyse and mutually compare time series of COVID-19-related data and mobility data across Belgium's 43 arrondissements (NUTS 3). In this way, we reach three conclusions. First, we could detect a decrease in mobility during high-incidence stages of the pandemic. This is expressed as a significant change in the average amount of time spent outside one's home arrondissement, investigated over five distinct periods, and in more detail using an inter-arrondissement ``connectivity index'' (CI). Second, we analyse spatio-temporal COVID-19-related hospitalisation time series, after smoothing them using a generalise additive mixed model (GAMM). We confirm that some arrondissements are ahead of others and morphologically dissimilar to others, in terms of epidemiological progression. The tools used to quantify this are time-lagged cross-correlation (TLCC) and dynamic time warping (DTW), respectively. Third, we demonstrate that an arrondissement's CI with one of the three identified first-outbreak arrondissements is correlated to a significant local excess mortality some five to six weeks after the first outbreak. More generally, we couple results leading to the first and second conclusion, in order to demonstrate an overall correlation between CI values on the one hand, and TLCC and DTW values on the other. We conclude that there is a strong correlation between physical movement of people and viral spread in the early stage of the SARS-CoV-2 epidemic in Belgium, though its strength weakens as the virus spreads