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

Starting early February 2020, 59 airline companies suspended or limited flights to Mainland China and a number of countries including USA, Russia, Australia, and Italy have also imposed government issued travel restrictions (23; 24; 25; 26; 27; 28) . It is difficult to calculate exactly the level of traffic reduction imposed by these measures. For this reason, we analyze here two major scenarios in which travel restrictions produce a 40% and 90% overall traffic reduction to and from China. The same traffic reductions are also applied domestically in China. Along with travel reductions, we consider three scenarios concerning disease transmissibility: i) a status quo situation with the same transmissibility found from the model calibration through January 23, 2020; ii) a moderate relative reduction of the original transmissibility (25%), corresponding to a transmissibility dampening factor of r = 0.75; and iii) a high reduction (50%) of the original transmissibility (r = 0.50). This relative reduction of transmissibility could be achieved through early detection and isolation of cases, as well as behavioral changes and awareness of the disease in the population. In Fig. 4 we show the combined effects of the travel and transmissibility reductions on the epidemic incidence in Mainland China and the number of exported cases to other countries. The simulated scenarios show that even in the case of drastic travel reductions (Fig. 4D) , if tranmissibility is not reduced (r = 1), the epidemic in China is delayed for no more than 2 weeks. The peak of the epidemic in Mainland China is reached at the end of April -early May, 2020. It is worth remarking that the epidemic peak in Wuhan in the absence of transmissibility reductions falls in the first week of March 2020. The number of cases imported to other countries, Fig. 4A -C, is initially affected by a tenfold reduction, but by March 1st 2020 when there is no transmissibility reduction (r = 1), this number has reached again the levels of 133 and 22 cases per day for the 40% and 90% travel restrictions scenarios, respectively. The concurrent presence of both travel and transmissibility reductions, however, produce a much larger synergistic effect visible by both delaying the epidemic activity in Mainland China and the number of imported cases. In the moderate transmissibility reduction scenarios (r = 0.75) the epidemic peak is delayed to late June 2020 and the total number of international case importations by March 1st 2020 are 21 and 3 cases per day for the 40% and 90% travel restrictions scenarios, respectively. Larger travel limitations (> 90%) will extend the period of time during which the importation of cases is greatly reduced. The 6 . CC-BY-NC-ND 4.0 International license It is made available under a author/funder, who has granted medRxiv a license to display the preprint in perpetuity. Flows are proportional to the relative probability that any one imported case will be traveling from a destination to a target.