Estimating a breakpoint in the spread pattern of COVID-19 in South Korea

Kim, Young-Joo; Seo, Myung Hwan; Yeom, Hyun-E

OBJECTIVES: Amid the global COVID-19 crisis, South Korea has been touted for successfully preventing the spread of the infectious disease, which may be due to the aggressive implementation of preventive policies. We evaluated the spread pattern of COVID-19 in South Korea considering the potential impact of policy interventions on transmission rates. METHODS: The SIR (Susceptible-Infected-Removed) model with a breakpoint that allows a change in transmission rate at an unknown point was proposed. Estimated trajectories of COVID-19 from SIR models with and without a breakpoint were compared. RESULTS: The proposed model with a break fitted the actual series of infection case much better than the classic model. The estimated breakpoint was March 7(th) and the transmission rate dropped by 0.23 after the breakpoint. A counterfactual study based on our estimate indicated that the number of the infected could reach 2,500,000 compared to the peak of 8,000 in the observed series. CONCLUSIONS: It is critical to consider a change in the transmission rate to evaluate the spread trajectory of COVID-19 in South Korea. Our estimation and counterfactual experiments indicate that public health interventions may play a role in determining the spread pattern of infectious diseases.