COVID-19 control across urban-rural gradients
Authors: Wells Konstans , Lurgi Miguel , Collins Brendan , Lucini Biagio , Kao Rowland R. , Lloyd Alun L. , Frost Simon D.W. , Gravenor Mike B. 
Published: September 2020

AbstractControlling the regional re-emergence of SARS-CoV-2 after its initial spread in ever-changing personal contact networks and disease landscapes is a challenging task. In a landscape context, contact opportunities within and between populations are changing rapidly as lockdown measures are relaxed and a number of social activities re-activated. Using an individual-based metapopulation model, we explored the efficacy of different control strategies across an urban-rural gradient in Wales, UK. Our model shows that isolation of symptomatic cases, or regional lockdowns in response to local outbreaks, have limited efficacy unless the overall transmission rate is kept persistently low. Additional isolation of non-symptomatic infected individuals, who may be detected by effective test and trace strategies, is pivotal to reduce the overall epidemic size over a wider range of transmission scenarios. We define an ‘urban-rural gradient in epidemic size’ as a correlation between regional epidemic size and connectivity within the region, with more highly connected urban populations experiencing relatively larger outbreaks. For interventions focused on regional lockdowns, the strength of such gradients in epidemic size increased with higher travel frequencies, indicating a reduced efficacy of the control measure in the urban regions under these conditions. When both non-symptomatic and symptomatic individuals are isolated or regional lockdown strategies are enforced, we further found the strongest urban-rural epidemic gradients at high transmission rates. This effect was reversed for strategies targeted at symptomatics only. Our results emphasise the importance of test-and-tracing strategies and maintaining low transmission rates for efficiently controlling COVID19 spread, both at landscape scale and in urban areas.Author summaryThe spread of infectious diseases is the outcome of contact patterns and involves source-sink dynamics of how infectious individuals spread the disease through pools of susceptible individuals. Control strategies that aim to reduce disease spread often need to accept ongoing transmission chains and therefore, may not work equally well in different scenarios of how individuals and populations are connected to each other. To understand the efficacy of different control strategies to contain the spread of COVID19 across gradients of urban and rural populations, we simulated a large range of different control strategies in response to regional COVID19 outbreaks, involving regional lockdown and the isolation individuals that express symptoms and those that developed not symptoms but may contribute to disease transmission. Our results suggest that isolation of asymptomatic individuals through intensive test-and-tracing is important for efficiently reducing the epidemic size. Regional lockdowns and the isolation of symptomatic cases only are of limited efficacy for reducing the epidemic size, unless overall transmission rate is kept persistently low. Moreover, we found high overall transmission rates to result in relatively larger epidemics in urban than in rural communities for these control strategies, emphasising the importance of keeping transmission rates constantly low in addition to regional measures to avoid the disease spread at large scale.