Assessing the impact of reduced travel on exportation dynamics of novel coronavirus infection (COVID-19)

Asami Anzai; Tetsuro Kobayashi; Natalie M. Linton; Ryo Kinoshita; Katsuma Hayashi; Ayako Suzuki; Yichi Yang; Sungmok Jung; Takeshi Miyama; Andrei R. Akhmetzhanov; Hiroshi Nishiura

In Figure 1 , a total of 242 cases were diagnosed and reported outside of China in 27 countries between Day 43 (13 January) and Day 67 (6 February 2020). Of these, 140 cases were considered to have been infected in China and 102 cases were considered to have been infected outside China. The country with the highest number of exported cases infected inside China was Thailand (n=20), followed by Singapore (n=18), Australia (n=14), and Japan (n=12). Among 242 cases, we specifically focus on 140 cases who traveled while movement restrictions were in place and were likely affected by said restrictions. Figure 2 compares the observed and expected number of cases diagnosed outside China by date of report. The exponential growth of cases is consistent with the exponential growth of incidence in China, which qualitatively captures the observed pattern of incidence from Day 43 to Day 57. Using the predicted curve, the expected number of cases between Day 58 (28 January 2020) and Day 67 was 321 cases (95% confidence interval [CI]: 181, 544). In the empirical observation, a total of 95 cases were diagnosed, including 8 cases in Japan. That is, following the time that Wuhan city was put in lockdown, we estimate that 226 cases (95% CI: 86, 449) were prevented from being exported across the world. This corresponds to a reduction in the number of exported cases of 70.4% during that time period.