Evaluation of the exit screening policy among travelers arriving from Asian and pacific nations

Abstract

Background: The Japanese government has instituted border control measures against COVID-19, including entry and exit screening of people arriving from overseas. We sought to evaluate the effectiveness of the exit screening policy in Japan in reducing the risk of importing COVID-19 cases among travelers from Asian and Pacific countries.

Methods: The study period was stratified based on the timing of exit screening: (i) the control period (the pre-exit screening period from 25 October 2020 to 16 January 2021), (ii) the time period with the Alpha variant from 17 January to 10 April 2021, and (iii) the time period with the Delta variant from 2 May to 2 October 2021. Incidence data in the countries of origin were used to adjust for the risk of infection among travelers. The positivity rate of entry screening in Japan was compared among the three different study periods, adjusting for the risk of infection in the country of origin.

Results: The adjusted relative risk of positivity was greatly reduced and substantially below the value of 1 during the Alpha variant period compared with the control period. Although the relative risks increased when comparing the Delta variant period against control, the estimate remained below 1, except for among travelers from India and Myanmar. The relative risk reduction was greatest in high-income countries, with estimates of 100% and 96% risk reduction during the Alpha and Delta variant periods, respectively, followed by upper-middle-income countries with estimates of 90% and 76%, respectively.

Conclusions: Even in the presence of the Alpha and Delta variants, exit screening clearly reduced the risk of infection among travelers arriving from Asian and Pacific nations. As the testing relies on the country of origin, the effectiveness varied greatly by the socioeconomic income status and epidemiological situation of those countries. Test standardization and quality assurance may be required in low- and middle-income countries.

Keywords: Border control; Effectiveness; Quarantine; Severe acute respiratory syndrome coronavirus 2; Southeast Asia; Statistical estimation; Travel; Western Pacific.

Fig. 1

Epidemic dynamics of COVID-19 in Japan, 2020–21. Border control policy changes were overlaid with variant-proportionated domestic weekly cases in Japan from October 2020 to December 2021. The purple gradient bar at the top represents, from left to right, the control period, the Alpha variant period, and the Delta variant period. The areas between the vertical lines indicate the study periods among foreign travelers. The different colors on the bar represent the proportions of cases attributed to different variants of concern owing to local transmission in Japan

Fig. 2

Relative risks of COVID-19 among Japanese travelers returning from nine countries during the Alpha and Delta periods compared with the control period, 2020–21. Relative risks of nine countries during (A) the Alpha variant period and (B) the Delta variant period. The risk in these periods with exit screening was compared against the risk during the control period without exit screening practice among Japanese nationals. For both periods, the dashed line signifies a relative risk value of 1 (i.e., no indication of the effectiveness of exit screening). Upper bound values among certain countries are shown as numerical numbers on the whisker. In the unadjusted prevalence ratio columns, values inside parentheses represent the corresponding 95% confidence intervals derived from binomial distribution

Fig. 3

Relative risk reductions of COVID-19 among returning Japanese by country income level category. Relative risk reductions during (A) the Alpha variant period and (B) the Delta variant period among Japanese travelers returning from high-income, upper-middle-income, and lower-middle-income countries are shown. Extremely small lower bound values for certain countries are shown on the whisker. Within the adjusted prevalence ratio column, values in parentheses indicate the corresponding 95% confidence intervals derived from binomial distribution

Fig. 4

Relative risk reductions of COVID-19 among non-Japanese travelers arriving from Asian countries, 2020–21. Relative risk reductions during (A) the Alpha variant period and (B) the Delta variant period among non-Japanese travelers arriving from China, South Korea and Sri Lanka are shown. Numeric lower bounds are provided for specific countries with extremely small values, and the adjusted prevalence ratio column includes values within parentheses denoting the corresponding 95% confidence intervals derived from binomial distribution