Temporal changes in the risk of superspreading events of coronavirus disease 2019 (preprint)

In order to identify the temporal change in the possible risk of superspreading events (SSE), we estimated the overdispersion parameter in two different periods of COVID-19 pandemic. We identified the possible risk of SSE was reduced 34% during the second epidemic period in South Korea.

Transmission Dynamics and Control of Two Epidemic Waves of SARS-CoV-2 in South Korea (preprint)

Background: After relaxing social distancing measures, South Korea experienced a resurgent second epidemic wave of coronavirus disease 2019 (COVID-19). In this study, we aimed to identify the transmission dynamics of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections and assess the impact of COVID-19 case finding and contact tracing in each epidemic wave.Methods: We collected data on COVID-19 cases published by local public health authorities in South Korea and divided the study into two epidemic periods (19 January–19 April 2020 for the first epidemic wave and 20 April–11 August 2020 for the second epidemic wave). To identify changes in the transmissibility of SARS-CoV-2, the daily effective reproductive number (Rt) was estimated using the illness onset of the cases. Furthermore, to identify the characteristics of each epidemic wave, frequencies of cluster types were measured, and age-specific transmission probability matrices and serial intervals were estimated. The proportion of asymptomatic cases and cases with unknown sources of infection were also estimated to assess the changes of infections identified as cases in each wave.Results: In early May 2020, within 2-weeks of a relaxation in strict social distancing measures, Rt increased rapidly from 0.2 to 1.8 within a week and was around 1 until early July 2020. In both epidemic waves, the most frequent cluster types were religious-related activities and transmissions among the same age were more common. Furthermore, children were rarely infectors or infectees, and the mean serial intervals were similar (~3 days) in both waves. The proportion of asymptomatic cases at presentation increased from 22% (in the first wave) to 27% (in the second wave), while the cases with unknown sources of infection were similar in both waves (22% and 24%, respectively).Conclusions: Our study shows that relaxing social distancing measures was associated with increased SARS-CoV-2 transmission despite rigorous case findings in South Korea. Along with social distancing measures, the enhanced contact tracing including asymptomatic cases could be an efficient approach to control further epidemic waves.

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

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.Interpretation: 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.Funding: This study was supported by the Basic Science Research Program through the National Research Foundation of Korea funded by the Korean Ministry of Education (NRF2020R1I1A3066471).Declaration of Interests: BJC reports honoraria from Sanofi Pasteur and Roche. All other authors declare no competing interests.Ethics Approval Statement: This study did not require institutional review board approval or informed consent, because all data used were anonymous and publicly available on local public health agency websites.

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

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.