ObjectivesTo compare the number and incidence of Kawasaki disease (KD) patients in years 2 through 4 of the coronavirus disease 2019 (COVID-19) pandemic, and determine the impact of 3 years of implementation infection control measures and their subsequent relaxation on the epidemiology of KD in Japan. Study designWe conducted a population-based, cohort study including consecutive KD patients in Kobe City between 2021 and 2023. We compared the incidence of KD cases, in relation to timing of infection control measures, as well as infectious disease cases based on a regional surveillance system. Data from a previous 2016 through 2020 study were used for comparison. ResultsA total of 566 children with KD were identified during the study period. During the infection control period in 2021 to 2022, the incidence of KD remained low compared with the pre-pandemic level (281.3 and 327.5/100,000 children aged 0-4 years in 2021to 2022 and 2016 through 2019, respectively), but a recovery trend began in the 0-1-year age group. During the relaxation period in 2023, the incidence of KD increased across a wide age range, reaching the highest recorded in Japan (426.7/100,000 children aged 0-4 years), and the median age of onset increased to age 30 months. The resurgence of KD coincided with the patterns for multiple infectious diseases in 2023. The seasonality of KD observed before the pandemic was altered. ConclusionsKD resurged in 2023 after relaxation of the prolonged COVID-19 pandemic restrictions in Japan. This phenomenon coincided with the rise of multiple infectious diseases, and supports the pathogenesis of KD being triggered by infectious agents.