Study population and setting
Using publicly available, de-identified population mobility data and data on disease importation, study authors modeled the domestic (within-China) and international spread of COVID-19. Authors also estimated the effects of the travel ban implemented in Wuhan (airport shutdowns beginning on January 23, 2020), mobility restrictions in Mainland China, and other travel restrictions adopted by other countries in early February 2020.
Summary of Main Findings
The model showed a reduction of 10% in cumulative cases within Mainland China by January 31, 2020 as a result of the Wuhan travel ban, relative to the counterfactual scenario of no restrictions. Authors assumed a doubling time (the period required for the number of cases in the epidemic to double) of 4-5 days, so this reduction corresponds to a delay in the epidemic trajectory of only 1-6 days. Furthermore, using WHO situational reports, authors estimated that only 1 in 4 infections are detected and confirmed in Mainland China. Authors estimated that 86% of international cases originated from Wuhan before the ban, and immediately after the ban, cases imported from Mainland China to other countries were reduced by 77%. However, this reduction was not sustained, and internationally imported cases rose again in the following weeks (mainly from Shanghai, Beijing, and Shenzhen). Finally, authors estimated case reduction through various combinations of travel restrictions and other interventions aimed at reducing transmissibility. Results indicate that even 90% travel reductions could at best delay the epidemic by no more than two weeks, without significant reductions in transmissibility from other measures.
This study estimated spread of COVID-19 using real-world mobility data. Authors independently validated the model by comparing model projections of cumulative number of cases across Mainland China with WHO situational reports; model projections were highly correlated with observed data.
Information used by the model regarding transmission (e.g., generation time– the time between source and recipient infections) are based on early results of the COVID-19 outbreak and epidemiology of SARS-CoV-1 and MERS; these parameters have changed as knowledge of SARS-CoV-2 has evolved. The models assumed homogeneous susceptibility and contact patterns by age, which may in fact vary considerably. Containment measures implemented prior to travel restrictions (e.g., body temperature screenings for departure in Wuhan International Airport) were not included in the model. Authors assumed long-term enforcement of travel restrictions in Wuhan through June 2020, which as of April 2020, is no longer applicable.
Effective national and international public health response planning depends on robust assessments of the effects of travel restrictions and other interventions. Results from this study indicate that the Wuhan travel ban delayed the spread of SARS-CoV-2, but was of modest utility as the epidemic continued, suggesting ongoing responses should focus on mitigation rather than containment.