JMIR Publications

ABSTRACT

Background:

Despite recent achievements in vaccines, antiviral drugs, and medical infrastructure, the emergence of coronavirus disease (COVID-19) has posed a serious threat to humans worldwide. Most countries are well connected on a global scale, making it nearly impossible to implement perfect and prompt mitigation strategies for COVID-19 outbreaks. In particular, due to the explosive growth of international travel, the diverse networks and complexities of human mobility have become essential factors that give rise to the rapid spread of COVID-19 globally.

Objective:

South Korea is one of the countries that experienced the early stage of the COVID-19 pandemic. In the absence of vaccines and treatments, South Korea has implemented and maintained stringent interventions, such as large-scale epidemiological investigations, rapid diagnosis, social distancing, and prompt clinical classification of severe patients with appropriate medical measures. In particular, South Korea has implemented effective airport screenings and quarantine measures. In this study, we aimed to assess the country-specific importation risk of COVID-19 and investigate its impact on the local transmission of COVID-19.

Methods:

The country-specific importation risk of COVID-19 in South Korea was assessed. We investigated the relationship among country-specific imported cases, passengers, and the severity of country-specific COVID-19 prevalence from January to October 2020. We assessed the country-specific risk by incorporating country-specific information. A renewal mathematical model was employed, considering both imported and local cases of COVID-19 in South Korea. Furthermore, we estimated the basic and effective reproduction numbers.

Results:

The risk of importation from China was the highest between January and February 2020, while that from North America (the United States and Canada) was significantly high from April to October 2020. The R_0 was estimated at 1.87 (95% confidence interval: 1.47, 2.34), with the rate (α =0.07) of the secondary transmission caused by the imported cases. The R_t was estimated in South Korea and in Seoul and Gyeonggi, respectively.

Conclusions:

A statistical model accounting for imported and locally transmitted cases was employed to estimate R_0 and R_t. Our results indicated that the prompt implementation of airport screening measures (contact tracing with case isolation and quarantine) successfully reduced local transmission caused by imported cases despite passengers arriving from high-risk countries throughout the year. Moreover, various mitigation interventions, including social distancing and travel restrictions within South Korea, have been effectively implemented to reduce the spread of local cases in South Korea.