The effect of travel restrictions on the spread of the 2019 novel coronavirus (2019-nCoV) outbreak

Matteo Chinazzi; Jessica T. Davis; Marco Ajelli; Corrado Gioannini; Maria Litvinova; Stefano Merler; Ana Pastore y Piontti; Luca Rossi; Kaiyuan Sun; Cécile Viboud; Xinyue Xiong; Hongjie Yu; M. Elizabeth Halloran; Ira M. Longini; Alessandro Vespignani

To model the international spread of the 2019-nCoV outbreak we use the Global Epidemic and Mobility Model (GLEAM), an individual-based, stochastic, and spatial epidemic model (4; 5; 6; 7). GLEAM uses a metapopulation network approach integrated with real-world data, where the world is divided into sub-populations centered around major transportation hubs (usually airports). The subpopulations are connected by the flux of individuals traveling daily among them. The model includes over 3,200 sub-populations in roughly 200 different countries and territories. The airline transportation data consider daily origin-destination traffic flows from the Official Aviation Guide (OAG) and IATA databases (updated 2019), while ground mobility flows are derived by the analysis and modeling of data collected from the Offices of Statistics for 30 countries on 5 continents (5) . Within each sub-population, the human-to-human transmission of 2019-nCoV is modeled using a compartmental representation of the disease where individuals can occupy one of the following compartments: Susceptible (S), Latent (L), Infectious (I) and Recovered (R). Susceptible individuals can acquire the virus through contacts with individuals in the infectious compartment, and become latent, meaning they are infected but can not transmit the disease yet. Latent individuals progress to the infectious stage with a rate inversely proportional to the latent period (which we assume to have the same duration as the incubation period), and infectious individuals progress into the removed stage with a rate inversely proportional to the infectious period. The sum of the mean latent and infectious periods defines the generation time. Removed individuals represent those who can no longer infect others, meaning they are recovered, isolated, hospitalized, or dead.