Institutional infrastructure provides a context for leadership to implement its policies. Yet prior studies on South Korea's successful COVID-19 response have focused primarily on the administration's leadership, the Korea Disease Control and Prevention Agency (KDCA), and the learning effects from Middle East respiratory syndrome (MERS). Using South Korea as a case study, this paper introduces a theoretical framework that captures various institutional determinants to explain its COVID-19 response. Applying Williamson's (2000) theoretical framework on the four layers of social institutions, we show how two institutional infrastructures—Confucian and collective norms and legacies of the business-government networks—may have contributed to South Korea's COVID-19 response through policy compliance, supportive R&D policies and inter-ministry collaboration. One of the key implications of our research lies in the learning effects of MERS, which may have been limited without institutional infrastructure like business-government networks.