Enhanced infectious disease surveillance system for Expo 2025 Osaka, Kansai, Japan: Overview of the operations and their early action review

The Osaka–Kansai Expo Infectious Disease Information Analysis Center (Expo ID Information Center) was established in Osaka as a temporary collaborative framework to facilitate epidemic intelligence activities for Expo 2025 Osaka, Kansai, Japan (Expo 2025), a long-term, large-scale international event that unites numerous municipalities and stakeholders for coordinated disease monitoring. This report provides an overview of this unique initiative and the results of an early action review (EAR) of the center’s operations. The operations, which began three months before the Expo 2025 opened, analyzed data on enhanced surveillance for risk assessment, response coordination, and information dissemination within Osaka and its surrounding municipalities. Five information sources were integrated for enhanced surveillance: national infectious disease surveillance, syndromic surveillance related to Expo 2025 stakeholders, vector mosquito monitoring, pharmacy-based influenza estimates, and media information. To identify operational challenges and improve processes, the center conducted a scenario-based EAR on-site with its members and relevant stakeholders two weeks after it started and approximately 10 weeks before the Expo opened, focusing on detection, verification, and response. Key improvement measures identified and implemented before the opening of Expo 2025 included establishing a data collection mechanism for timely detection, developing clear criteria for reporting unusual/unexpected events, defining stakeholder communication focal points and pathways, particularly outside official working hours, and clarifying stakeholders’ responsibilities and command structure. By conducting this EAR, operational challenges were identified early and corrected, and mutual understanding of this new framework was promoted among stakeholders through direct engagement. The Expo 2025 Osaka, Kansai, Japan (Expo 2025), held from April to October of 2025, is a large-scale international mass gathering event expected to attract over 28 million visitors, including 3.5 million from overseas [1] . In events such as this, the host country, local governments, and event organizers must cooperate, anticipate disease potential outbreaks, and strengthen their epidemic intelligence capabilities. Japan has recently hosted several international mass gatherings and high-profile events and has improved its epidemic intelligence capabilities. For Expo 2025, the national and local governments conducted infectious disease risk assessments and enhanced the surveillance system, in line with responses to previous events, including the G20 Osaka Summit (2019), the 2019 Rugby World Cup (2019), Tokyo 2020 Olympic and Paralympic Games (2021) [2] , and the G7 Hiroshima Summit (2023). However, unlike these previous events, Expo 2025 represents the first large-scale international mass gathering in Japan since the COVID-19 pandemic, spanning 6 months and involving numerous municipalities and stakeholders. Thus, the Osaka Institute of Public Health (OIPH), Osaka Prefectural Government (OPG), and Osaka City Public Health Center (OCPHC), in collaboration with the National Institute of Infectious Diseases and Japan Institute of Health Security (NIID-JIHS), including the Field Epidemiology Training Program (FETP) [3] , established an ad hoc organization, the Osaka-Kansai Expo Infectious Disease Information Analysis Center (the Expo ID Information Center), to serve as the central hub for epidemic intelligence during Expo 2025. This report provides an overview of this unique initiative and shares results of an early action review (EAR) of the Expo ID Information Center’s operations.