Jun 5, 2020
By January 31, 2020, at Least 1.5 Daily Infected Passengers Were Originating in China
By January 31, 2020, passengers from China were likely exporting at least 1.5 cases of COVID-19 globally per day. The eight countries most at risk of infection, based on our modeling, were Japan, Thailand, South Korea, the United States, Taiwan, Australia, Singapore, and Malaysia. These were also the eight countries with the most confirmed cases outside of China as of January 31, 2020.
In this report—one of several from a RAND Corporation team examining the role of commercial air travel in the coronavirus disease 2019 (COVID-19) pandemic—we estimate the daily rate of virus transmission via air travel from China. By combining COVID-19 case data from Johns Hopkins University with detailed air travel data (including each passenger's origin and destination) from the International Air Transport Association, we can use our COVID-19 Air Traffic Visualization (CAT-V) tool to model the global risk of COVID-19 transmissions resulting from commercial air travel.
By late January 2020, infections of COVID-19 were likely being exported from China, via commercial air travel, every day—even based on China's reported COVID-19 caseload of fewer than 10,000 by January 31, 2020 (see the caveats section). Because China has a population of more than 1.4 billion, this confirmed caseload means that only one in 150,000 residents was officially reported as having the novel coronavirus. When we combine that information with data on air travel to a given country, we can estimate the rate of virus transmission through air travel. For example, more than 1 million people, or more than 32,000 per day, traveled from China to Japan in January 2020. So, the ratio of one in 150,000 Chinese travelers being infected translates to an expected rate of infection exportation to Japan of about one every five days.
When we consider China's reported caseload on a global scale, there were at least 1.5 daily infected air travel passengers originating in China and dispersing worldwide by January 31, 2020.
Using the CAT-V tool, we identified the eight countries with the highest risk of importing COVID-19 from China on January 24, 2020. These countries, in descending order of risk, were Japan, Thailand, South Korea, the United States, Taiwan, Australia, Singapore, and Malaysia (see the map below). On January 31, 2020, these same countries indeed had the most confirmed COVID-19 cases outside of China.
More specifically, Japan, Thailand, and South Korea—the three countries with the highest risk on January 24, 2020—were among the four countries with the most confirmed COVID-19 cases outside of China one week later.
In accordance with RAND's quality assurance standards, this analysis is based on the best available data. However, COVID-19 is an evolving threat, and even the best available data being used by government agencies and research institutes have significant limitations. In the first report in this series, we outline several caveats about using country-level data, assuming equal passenger risk profiles, drawing on inaccurate country caseload reports, and being restricted by other data limitations.
For this report, it is important to reiterate that the CAT-V tool uses country-level data and thus assumes that the overall rates of international travel from China are comparable across the Chinese provinces. It is also important to reiterate that the tool, consistent with most academic research and public policy tools, uses confirmed COVID-19 cases, as reported by individual countries. The true number of infected individuals in any given country is certainly higher than reported. The CAT-V tool does not correct for inaccurate or misleading case reporting.