Population Density and Spreading of COVID-19 in England and Wales

TL;DR

This study analyzed COVID-19 spread in England and Wales over 15 months, revealing how population density and public health measures influenced regional outbreak dynamics, variance, and skewness in case and death data.

Contribution

It introduces density scaling models to understand regional COVID-19 propagation and highlights the impact of lockdowns, school reopenings, and holidays on outbreak heterogeneity.

Findings

Lockdowns and school reopenings increased variance, indicating outbreaks and regional heterogeneity.

Holidays and university reopenings reduced variance, suggesting homogenization of spread.

Rural regions showed consistent death metrics, linked to regional demographics.

Abstract

We investigated daily COVID-19 cases and deaths in the 337 lower tier local authority regions in England and Wales to better understand how the disease propagated over a 15-month period. Population density scaling models revealed residual variance and skewness to be sensitive indicators of the dynamics of propagation. Lockdowns and schools reopening triggered increased variance indicative of outbreaks with local impact and country scale heterogeneity. University reopening and December holidays triggered reduced variance indicative of country scale homogenisation which reached a minimum in mid-January 2021. Homogeneous propagation was associated with better correspondence with normally distributed residuals while heterogeneous propagation was more consistent with skewed models. Skewness varied from strongly negative to strongly positive revealing an unappreciated feature of community propagation. Hot spots and super-spreading events are well understood descriptors of regional disease dynamics that would be expected to be associated with positively skewed distributions. Positively skewed behaviour was observed; however, negative skewness indicative of cold-spots and super-isolation dominated for approximately 8 months during the period of study. In contrast, death metrics showed near constant behaviour in scaling, variance, and skewness metrics over the full period with rural regions preferentially affected, an observation consistent with regional age demographics in England and Wales. Regional positions relative to density scaling laws were remarkably persistent after the first 5-9 days of the available data set. The determinants of this persistent behaviour probably precede the pandemic and remain unchanged.