A data-driven assessment of early travel restrictions related to the spreading of the novel COVID-19 within mainland China

Alberto Aleta; Qitong Hu; Jiachen Ye; Peng Ji; Yamir Moreno

The copyright holder for this preprint . https://doi.org/10.1101/2020.03.05.20031740 doi: medRxiv preprint 1 2 -J a n 1 7 -J a n 2 2 -J a n 2 7 -J a n 1 -F e b 6 -F e b 1 1 -F e b 1 6 -F e b A Spring Festival Travel Restrictions -100 0 200 400 600 0 1 -J a n 0 6 -J a n 1 1 -J a n 1 6 -J a n 2 1 -J a n 2 6 -J a n 3 1 -J a n 5 -F e b 1 2 -J a n 1 7 -J a n 2 2 -J a n 2 7 -J a n 1 -F e b 6 -F e b 1 1 - 0 1 -J a n 0 6 -J a n 1 1 -J a n 1 6 -J a n 2 1 -J a n 2 6 -J a n 3 1 -J a n 5 - this period of the year has some peculiarities due to the Spring Festival, an event that completely modifies the travel patterns of the population. In 2020, the Spring Festival was celebrated on Jan. 25th, while in 2019 it took place on Feb. 5th. For this reason, we align both simulations so that "day 0" will correspond in both years to the day of the Spring Festival (Jan. 25th and Feb. 5th respectively). As a consequence, we start the simulations on Jan. 12th, 2019 and Jan. 1st, 2020, so that in both years the period between the first reported cases and the celebration of the Spring Festival is the same. Lastly, the simulation will run in both cases to 13 days after the Festival, which corresponds to Feb. 5th in 2020 and Feb. 16th in 2019. Fig. 1 clearly shows that the changes induced by the epidemic in the overall flow and movement of the population throughout China is not restricted just to the region in which the city of Wuhan is located (Hubei). In 2019, a large number of individuals moved right before the Spring Festival. Then, it reached a minimum at the Spring Festival and later on, again, a large number of individuals moved again, see Fig. 1A . On the other hand, in 2020, the situation was similar only until Jan. 23rd, when the travel restrictions in Wuhan were implemented. Two features are worth highlighting. First, when the travel restrictions were implemented, the flow of population had peaked already just before the Spring festival. This is key to understand why, despite the reduction in mobility, the daily number of new cases have continued to increase for weeks. Secondly, most of the second wave observed in 2019 − which corresponds to travel back to the original region− might have not taken place yet (see Fig. 1B ), and thus, there is still a high risk that a subsequent large outbreak or increase in the number of newly infected individuals happens. The existence of recurrent local outbreaks is a feature that some models have anticipated [20] . Further indications that the population has not yet reached the original distribution by region are provided in Figs. 1C and 1D , where we show the number of individuals living in each region at the beginning of the simulation (initial data obtained from the Chinese Yearbook, see Materials and Methods) and at the end according to our data. Clearly, while in 2019 most of the population returned to their regions, in 2020 this has not taken place yet.