OBJECTIVES: We aimed to compare epidemiologic features of second and third COVID-19 pandemic waves in South Korea .

METHODS: Nationwide COVID-19 data was collected during the study period (May 6-December 30). The degree of social activities was also estimated using the internet searching trend analysis program for leisure-related keywords including``eating-out ,"`` trip ,"and``get directions"( transportation). We compared the demographics, transmission chains, case fatality rates, social activity level, and public health responses between second (August 13-September 18) and third (November 4-present) waves .

RESULTS: Compared to the second wave, the third wave was characterized by delayed social distancing reinforcement (3 vs. 15 days), longer duration (36 vs.> 56 days) and higher fatality rates (0.91% vs. 1.26 %). There was a significant difference in transmission chains of the second and third waves of the COVID-19 pandemic (p <0.01). During the third wave compared with the second wave, the proportion of local clusters (24.8% vs. 45.7 %) was lower, while those of personal contact transmission (38.5% vs. 25.9 %) and unknown routes of transmission (23.5% vs. 20.8 %) were higher .

CONCLUSION: Early and timely interventions with strengthened social distancing policies should be implemented to effectively suppress and control the COVID-19 pandemic.