Abstract
Assessing the impact of mobility on epidemic spreading is of crucial importance for understanding the effect of policies like mass quarantines and selective re-openings. While many factors affect disease incidence at a local level, making it more or less homogeneous with respect to other areas, the importance of multi-seeding has often been overlooked. Multi-seeding occurs when several independent (non-clustered) infected individuals arrive at a susceptible population. This can lead to independent outbreaks that spark from distinct areas of the local contact (social) network. Such mechanism has the potential to boost incidence, making control efforts and contact tracing less effective. Here, through a modeling approach we show that the effect produced by the number of initial infections is non-linear on the incidence peak and peak time. When case importations are carried by mobility from an already infected area, this effect is further enhanced by the local demography and underlying mixing patterns: the impact of every seed is larger in smaller populations. Finally, both in the model simulations and the analysis, we show that a multi-seeding effect combined with mobility restrictions can explain the observed spatial heterogeneities in the first wave of COVID-19 incidence and mortality in five European countries. Our results allow us for identifying what we have called epidemic epicenter: an area that shapes incidence and mortality peaks in the entire country. The present work further clarifies the nonlinear effects that mobility can have on the evolution of an epidemic and highlight their relevance for epidemic control.
Highlights
The COVID-19 epidemic reached the WHO status of pandemic on March 11, 2020 [1] and currently involves most of the countries of the world [2]
We address the question of how relevant is multi-seeding for an epidemic
Beyond the classical analysis centered on the arrival time of the first imported cases, here we focus on the effect that the incoming of more seeds have on the evolution of the local epidemic curves
Summary
The COVID-19 epidemic reached the WHO status of pandemic on March 11, 2020 [1] and currently involves most of the countries of the world [2]. In Europe, SARS-CoV-2 severely hit Italy, the first country to report local transmission in mid/late-February [3], and by mid March many other countries such as France [4], Germany [5], Spain [6] and the UK [7] declared local outbreaks as well. Measures to prevent the propagation of the disease were implemented, first locally, as closing schools and universities, public buildings, etc, and, secondly, at national level with a population confinement at home (lockdown) [8] implemented on March 14, 2020, which with different degrees of severity lasted until June 21, 2020. The initial phases of the lockdown included a reduction of the frequencies and capacities of public transportation lines, with the most strict mitigation measures taken between March 29 and April 23. The situation in the other European countries evolved more or less in parallel with some delays or advances depending on the local propagation patterns
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
