Comparison of the second and third waves of the COVID-19 pandemic in South Korea: Importance of early public health intervention.

• Epidemiologic features of the second and third waves of the coronavirus disease 2019 (COVID-19) pandemic in South Korea were compared. • Strengthening of social distancing policies was delayed in the third wave compared with the second wave. • The third wave persisted longer than the second wave, and had a higher case fatality rate. • Early public health intervention is important to control the COVID-19 pandemic. To compare epidemiologic features of the second and third waves of the coronavirus disease 2019 (COVID-19) pandemic in South Korea. Nationwide COVID-19 data were collected between 6 May and 30 December 2020. The degree of social activity was estimated using an Internet search trend analysis program for leisure-related keywords, including 'eating-out', 'trip' and 'get directions' (transportation). Demographics, transmission chains, case fatality rates, social activity levels and public health responses were compared between the second (13 August–18 September 2020) and third (4 November 2020–present) waves. In comparison with the second wave, the third wave was characterized by delayed strengthening of social distancing policies (3 vs. 15 days), longer duration (36 vs. >56 days) and a higher case fatality rate (0.91% vs. 1.26%). There were significant differences in transmission chains between the second and third waves (P < 0.01). In comparison with the second wave, the proportion of local clusters (24.8% vs. 45.7%) was lower in the third wave, and personal contact transmission (38.5% vs. 25.9%) and unknown routes of transmission (23.5% vs. 20.8%) were higher in the third wave. Early and timely interventions with strengthened social distancing policies should be implemented to suppress and control the COVID-19 pandemic effectively. [ABSTRACT FROM AUTHOR]