Moreover, many patients with asymptomatic infection had traveled to other regions, which caused the confirmed case numbers to increase exponentially at the early stage of the COVID-19 outbreak ( Tian et al., 2020).
Therefore, for an epidemic with the human-to-human transmission characteristic, extensive population flow has substantially increased social contacts in public, which caused COVID-19 to reach essentially everywhere ( Bherwani et al., 2020). As a contact transmission, the COVID-19 transmission is mostly due to person-to-person contact ( Baker et al., 2020). As of 08:00 am (GMT + 8) on 29 July 2020, it has affected 216 countries and territories, 16,523,815 have been confirmed positive for COVID-19, and 655,112 have died ( World Health Organization, 2020). Nowadays, coronavirus (COVID-19) is spreading quickly and globally. Our findings quantified the effectiveness of travel restrictions on delaying the epidemic growth and limiting the spread scope of COVID-19 in China, which helped better derive the geographical COVID-19 transmission related to population flow networks' structural features. By removing different influential spreaders, we identified Guangzhou can most influence the network's topological characteristics, and some major cities' degree centrality was significantly decreased. We built the population flow networks to analyze their Spatio-temporal characteristics and identify the influential sub-groups and spreaders. We built an importation risk model to identify some major cities (Dongguan and Foshan) with the highest total importation risk values and the highest standard deviations, indicating the core transmission chains (Dongguan-Shenzhen, Foshan-Guangzhou). We predicted some original (Guangzhou, Shanghai, Shenzhen) had higher total aggregate population outflows than Wuhan, indicating larger spread scopes and faster growth rates of COVID-19 outbreak. In this paper, we simulated 42 transmission scenarios to show the distribution of the COVID-19 outbreak across China.
Network analysis provides a new methodology to uncover the topology and evolution of the population flow and understand its influence on the early dynamics of COVID-19 transmission. Large-scale and diffuse population flow amplifies the localized COVID-19 outbreak into a widespread pandemic.
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