Disease control across urban–rural gradients

Abstract

Controlling the regional re-emergence of severe acute respiratory syndrome coronavirus 2 (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 reducing 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 symptomatic individuals only. Our results emphasize the importance of test-and-trace strategies and maintaining low transmission rates for efficiently controlling SARS-CoV-2 spread, both at landscape scale and in urban areas.

Simulating the impacts of interregional mobility restriction on the spatial spread of COVID-19 in Japan

“…The second aspect of control measures is whether interregional mobility restrictions can reduce the national total number of infections. Distinguishing between the short- and long-term control measures is important, and the fundamental goal should be toward reducing the overall epidemic size 22 . According to our simulation results, solely restricting interregional mobility has a limited effect on reducing the national total number of infectious individuals.…”

“…Imposing interregional mobility restrictions cuts the growth rate in national total number of infectious individuals only when the effective reproduction number is one or higher. Moreover, research in the UK indicates that regional lockdowns effectively reduced the overall epidemic size only when the transmission rate remains persistently low 22 . These results imply that the efficacy of imposing interregional mobility restrictions (in terms of reducing the overall epidemic size) is very sensitive to the timing of the restriction.…”

“…How interregional mobility restrictions limit the expansion of infection in Japan’s context is largely unknown, although many previous studies have emphasized the importance of understanding the spatial dynamics of spread 14 – 21 . Effective control measures that prevent spatial spread of SARS-CoV-2 are urgently demanded, and how NPIs such as travel restrictions and social distancing mitigate the epidemic must be investigated 22 – 31 .…”

“…The social interaction approach constructs a contact matrix across various categories defined on the basis of factors such as age and gender 24 , 29 , 31 , 33 – 35 . Similarly, person-to-person interactions across different regions are incorporated into the OD matrix 22 , 27 .…”

Health and social behaviour through pandemic phases in Switzerland: Regional time-trends of the COVID-19 Social Monitor panel study

“…A partial closure of borders to its neighbouring countries aimed to slow transmission rates in Switzerland during the first wave of the pandemic. An important driver for the pandemic is more densily populated areas like cities and surrounding areas leading to an urban-rural gradient [ 48 ]. In 2020, the percentage of individuals living in an urban area was estimated at 83% ( https://www.bfs.admin.ch/bfs/de/home/statistiken/kataloge-datenbanken/grafiken.assetdetail.12767388.html , accessed January 10, 2020).…”