INTRODUCTION:
On April 1, 2025, the National Center for Global Health and Medicine (NCGM) and the National Institute of Infectious Diseases (NIID) were merged to establish the Japan Institute for Health Security (JIHS). This reform aims to strengthen Japan’s capacity to address infectious diseases and other health threats, contributing to a more resilient and secure society. This paper reviews progress made during the first two years of JIHS.

METHODS:
We reviewed policy documents, government reform plans, and institutional frameworks to describe the background, governance structure, and strategic functions of JIHS.

RESULTS:
JIHS is organized around four strategic pillars: (1) disease intelligence, enhancing risk assessment and data analytics; (2) research, development, and innovation, accelerating scientific and medical advances; (3) comprehensive medical services, strengthening clinical response capacity; and (4) human resource development and international cooperation, fostering expertise and global partnerships. The integration of NCGM and NIID has created synergy between basic research and clinical practice, improved information sharing, and enabled more coordinated national responses. During its first two years, JIHS established domestic and Asian clinical trial networks and developed action plans outlining response strategies for future pandemics.

CONCLUSIONS:
JIHS represents a major reform in Japan’s health security system. By consolidating scientific expertise, clinical capacity, and international collaboration, JIHS is well positioned to enhance evidence-based policymaking, promote innovation, and strengthen preparedness and response to future domestic and global infectious disease threats. Continued collaboration with national and international partners will be essential to achieving these goals.