Epidemiology and Control of Two Epidemic Waves of SARS-CoV-2 in South Korea

Background: Since the first case of pandemic COVID-19 in South Korea, identified on 19 January 2020, two epidemic waves have occurred. We characterised the epidemiology, transmission dynamics and effectiveness of control measures in each epidemic wave of COVID-19.Methods: We analysed publicly available data on confirmed cases of COVID-19 outside of Daegu-Gyeongbuk Regions in South Korea during first (19 January–19 April 2020) and second (20 April–11 August 2020) epidemic waves. Transmissibility of SARS-CoV-2 was measured by daily effective reproductive number, Rt. Frequencies of cluster types, age-specific transmission probability matrices, proportion of asymptomatic and unlinked cases, and serial interval distribution were estimated for each wave. Results: In early May, within 2-weeks of relaxation on strict social distancing measures, Rt increased rapidly from 0.2 to 2.3 within a week and was around 1 until early July. The most frequent clusters type were the religious related activities in both waves, but noticed more workplace-related clusters in the second wave. The proportion of asymptomatic cases at presentation increased from 22% during first wave to 27% during second wave. The proportion of unlinked local cases were similar in both waves (22% and 24%). Transmissions among same age were more common, and children were rarely infectors or infectees. The mean serial interval were similar (~3 days) in both waves. Conclusions: Our study shows that relaxing social distancing measures was associated with increased SARS-CoV-2 transmission. Enhanced contact tracing including asymptomatic cases could be more efficient with social distancing to control further waves of the pandemic.