Study population and setting
China imposed complete lockdown on Wuhan city (January 23, 2020) and in 15 cities throughout Hubei province (January 24, 2020). The authors used daily case counts of COVID-19 in mainland China from December 8, 2019 to February 15, 2020 along with airline network data, to predict the volume of exported COVID-19 cases before and after the lockdowns, and under the counterfactual scenario of no restrictions. Using estimates of the incubation period and duration of the pre-isolation symptomatic period, the potential impacts of general airport screening (symptomatic or questionnaire-based) and contact tracing in China were also estimated from model-derived probabilities of COVID-19 cases traveling.
Summary of Main Findings
Travel lockdowns were estimated to reduce international exportation of COVID-19 cases by 71% (95% CI: 69%, 72%), from 779 to 230 cases. An estimated 82 additional exported cases from mainland China (95% CI: 72 to 95) were contained due to airport screening. Hypothetical quarantine following contact tracing in mainland China was estimated to have only a modest effect (25% reduction) on the probability of travel among infected cases.
A strength of the study was the inclusion of airline network data in the analysis. Key model parameters (e.g., incubation period) were estimated using the best available data.
The non-pharmaceutical interventions of airport screening, contact tracing, and quarantine are described and modeled in very general terms. Airline network data were outdated (from 2014). Authors address case under-reporting in China, but under-reporting of exportation events is also likely and thus affected model calibration.
The study integrates empirical COVID-19 incidence data from mainland China with airline network data in an attempt to isolate effect estimates for multiple, co-occurring nonpharmaceutical interventions– travel lockdowns, airport screening, and contact investigations.