Asia International Institute of Infectious Disease Control (ADC) collaborated with Teikyo University Hospital from April 19th, 2021 to December 28th, 2022 to analyze mutant strains in patients diagnosed as COVID-19 positive. Mutant strains have been observed to displace epidemics. The results of real-time RT-PCR analysis of specific mutations in positive specimens confirmed an epidemic pattern of mutant strains consistent with the waves of infection in Japan: The alpha strain (N501Y mutation) was prevalent in the fourth wave in 2021, the delta strain (L452R mutation) in the fifth wave from summer to fall, and replacement by the omicron strain (BA.1→BA.2→BA.5 strain) was observed after 2022.These results are consistent with the transition of the prevalent strains in Japan, and indicate the importance of mutant strain analysis in preventing nosocomial infections and improving public health in local communities. We will continue to strengthen collaboration between the affiliated hospitals and the institute to establish a rapid response system for new infectious diseases.

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