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

Abstract

Motivated by the rapid spread of a novel coronavirus (2019-nCoV) in Mainland China, we use a global metapopulation disease transmission model to project the impact of both domestic and international travel limitations on the national and international spread of the epidemic. The model is calibrated on the evidence of internationally imported cases before the implementation of the travel quarantine of Wuhan. By assuming a generation time of 7.5 days, the reproduction number is estimated to be 2.4 [90% CI 2.2-2.6]. The median estimate for number of cases before the travel ban implementation on January 23, 2020 is 58,956 [90% CI 40,759 - 87,471] in Wuhan and 3,491 [90% CI 1,924 - 7,360] in other locations in Mainland China. The model shows that as of January 23, most Chinese cities had already received a considerable number of infected cases, and the travel quarantine delays the overall epidemic progression by only 3 to 5 days. The travel quarantine has a more marked effect at the international scale, where we estimate the number of case importations to be reduced by 80% until the end of February. Modeling results also indicate that sustained 90% travel restrictions to and from Mainland China only modestly affect the epidemic trajectory unless combined with a 50% or higher reduction of transmission in the community.

Figure 1:

A) Trajectory of the 2019-nCoV epidemic in Chinese locations (excluding Wuhan) under the travel ban to and from Wuhan in effect as of January 23rd, 2020. The lines represent the median cumulative number of cases while the shaded areas represent the 90% reference range. B) Number of cases predicted by the model on February 5th as a function of the number cases observed in individual provinces in China by that date. The size of the circles are proportional to the population size in each province. C) Projections of the average total number (daily) of international case importations with and without travel ban from Wuhan. Observed data of international case importations with a travel history from Wuhan by arrival date. Shaded areas represent the 99% reference range.

Figure 2:

A) Relative reduction of incidence across China as of February 22, 2020. The color of circles represents the relative reduction in the number of cases, while the size represents the population in the region. B) Projected cumulative number of cases by the same date, after implementing travel restrictions in Wuhan.

Figure 3:

Contribution to the relative risk of importation of the top 10 Chinese cities (plus the rest of Mainland China) before and after the Wuhan travel ban. The listed countries correspond to the top 20 countries at risk of importation. Flows are proportional to the relative probability that any one imported case will be traveling from a destination to a target.

Figure 4:

Analysis of the combined effects of travel and transmissibility reductions on the epidemic. Median number of imported cases from Mainland China for different dampening factors of the original transmissibility (r) and travel reductions (TR) A) no transmissability reduction, TR ∈ {40%, 90%}; B) r = 0.75, TR ∈ {40%, 90%}; C) r = 0.5, TR ∈ {40%, 90%}. Shaded areas the 90% confidence interval. D) Incidence in Mainland China excluding Wuhan for the different scenarios considered in A-C