COVID-19 is an important new coronavirus infection. The disease it causes has been identified in more than 60 countries. ^{Reference Hsia1} Indochina was the second area with an identified case in the timeline of the COVID-19 pandemic and Thailand is the first area reporting the case outside China. ^{Reference Sriwijitalai and Wiwanitkit2} Screening for disease at international border posts was a national public health policy against COVID-19 implemented from January 2020 onward. The screening had apparent limitations, ^{Reference Sriwijitalai and Wiwanitkit2} as other countries still reported detection of COVID-19 in travelers from Indochina. ^{Reference Yasri and Wiwanitkit3} In this letter, the authors discuss the topic of COVID-19 exported to other countries, which can illustrate the challenges of emigration screening. According to data from local Immigration Bureau, 3338710 foreigners were screened for COVID-19 at the international emigration post. Regarding exportation of disease, at least 3 patients who had a history of traveling have been confirmed to have COVID-19. The rate of undetected COVID-19 cases at the emigration international border post is therefore 9 x 10⁻⁵% (95% confidence interval between 3 x 10^-5% and 2.8 x 10⁻⁴%). In the worst case scenario, 3 out of 1000000 travelers might carry COVID-19 to their next destination. Entrance or immigration screening is usually intensive, while exit or emigration screening is less strict. A good disease screening system for both immigration and emigration can promote early detection and prevent the international spread of COVID-19.