Impact of travel restrictions for travellers from China on the internal spread of SARS-CoV-2 in South Korea

Abstract

South Korea implemented restrictions on travel from China in January of 2023. In this scenario-based model, we estimated that the travel restrictions for inbound travellers from China were associated with a 0.3–9.8% decrease in the internal spread of SARS-CoV-2 in South Korea (95% Confidence Interval, 0.2–11.7%).

On 8 January 2023, Chinese authorities eased travel rules,¹ with the expectation that the number of Chinese travellers in 2023 would be two-thirds of 2019 levels.² On 2 January 2023, South Korea, a popular travel destination for Chinese travellers, asked inbound travellers from China to mandatorily submit a negative polymerase chain reaction (PCR) test result for severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) upon arrival in Korea (i.e. exit screening). However, 13% of travellers with negative test results from China tested positive on arrival in Korea.³ On 2 January 2023, Korean authorities suspended short-term visa issuance (i.e. travel restrictions) for inbound travellers from China (Table S1). Here, we assessed the impact of travel restrictions for inbound travellers from China on the internal spread of SARS-CoV-2 in Korea.

We collected the daily number of SARS-CoV-2 infections in Korea from 10 December 2022 to 9 January 2023,⁴ and reconstructed the daily number of infections using a deconvolution-based method (Supplementary Materials).⁵ Then, we estimated the daily effective reproduction number () to represent the average number of infections in an infected case at day t. The epidemic is considered to be under control if R_t remains < 1. We assumed that suspending visa issuance would not restrict travel by 9 January 2023, as travellers usually issue their visas before they travel. Based on the estimated of SARS-CoV-2, we assumed that the mean in Korea on 10 January 2023, was 0.85. We considered four scenarios for the daily number of travellers from China entering Korea without entry screening in Korea: 0 (under travel restrictions), 1000 (similar to early in the COVID-19 pandemic), 5000 and 10 000 (two-thirds of the 2019 levels). We further considered two different probability scenarios of travellers infected in China (10 and 30%) and the specificity of exit screening using a PCR test for SARS-CoV-2 conducted in China (90 and 70%) (Table S2). We used the Monte Carlo simulation to generate the probability distribution of each scenario for the daily number of SARS-CoV-2-infected travellers to Korea (Supplementary Materials). We also considered traveller's stay periods by following the period distribution provided by Korean Statistical Information (Table S5). Using this distribution, we projected the daily number of SARS-CoV-2 infections in Korea (Supplementary Algorithm 1) by 31 January 2023 (the date of relaxing mandatory wearing of face masks) and estimated the . Then, we estimated the impact of the travel restrictions by fitting a regression model for (Supplementary Materials).

Compared to the travel restriction scenario, we identified an increase in the number of SARS-CoV-2 infections for 1000, 5000 and 10 000 inbound travellers daily by 0.2–0.3%, 0.3–0.9% and 0.3–1.8%, respectively (Figure 1, Table S3). We also identified the travel restrictions were associated with a 0.3–2.3%, 1.3–7.2% and 2.5–9.8% decrease in the for 1000, 5000 and 10 000 inbound travellers, respectively (Table S4).

Figure 1.

The daily number of SARS-CoV-2 infections and effective reproduction number in South Korea by different scenarios for the different numbers of inbound travellers from China. The blue bars and grey lines indicate the daily number of SARS-CoV-2 infections and daily effective reproduction number (), respectively, in different scenarios. The scenarios include the numbers of inbounding travellers from China entering South Korea: 0 (travel restrictions, Figure 1), 1000 (Figure 1A), 5000 (Figure 1B) and 10 000 (Figure 1C) with different probabilities of being infected and specificity of exit screening tests for travellers from China. Vertical red bars indicate the assumed effective date of travel restriction by suspending short-term visa insurance for incoming travellers from China. The number of SARS-CoV-2 infections after 9 January 2023, was projected based on the different scenarios. The red circles with upper and lower bounds show the median estimate and 95% confidence intervals based on retrospectively observed SARS-CoV-2 infections (as of 10 February 2023).

Our findings suggest that a high volume of travellers from China had a limited impact on the number of infections and spread of SARS-CoV-2 in Korea. This is likely due to the high population immunity against SARS-CoV-2 in Korea (89% of the population had booster dose immunization and 98% of the overall population had antibodies against SARS-CoV-2 as of December 2022).⁶ Monitoring the volume of incoming travellers, circulating variants, the population immunity from the country at risk of infection and domestic population immunity against SARS-CoV-2 is warranted to develop optimal international travel measures.

Funding

This work was supported by the Basic Science Research Programme of the National Research Foundation of Korea of the Ministry of Education (NRF-2020R1I1A3066471).

Authors’ contributions

Sukhyun Ryu (Conceived the study), Changhee Han, Hayong Seo and Soojung Cho (Data Collection and Assimilation), Changhee Han, Hayong Seo, Soojung Cho, Achangwa Chiara and Sukhyun Ryu (Performed data analysis, discussed the results and drafted the manuscript), all authors have critically read and approved the final manuscript.

Conflicts of interest: All authors declare no competing interests.

Ethical approval and consent to participate

This study did not require institutional review board approval or informed consent, because all data used were anonymous and publicly available on websites.

Data availability

The data underlying this article will share on reasonable request to the corresponding author.