Activating laboratory surveillance response to the threat of H5N1 influenza in the Veterans Health Administration, 2024-25.

INTRODUCTION: The Veterans Health Administration (VHA) mobilized and adapted its established national infrastructure to enhance influenza surveillance during 2024-2025 highly pathogenic avian influenza (HPAI) A(H5N1) panzootic. Additionally, VHA's Public Health Reference Laboratory (PHRL) expanded capacity for H5 subtyping and whole genome sequencing (WGS) to support detection. METHODS: Routine influenza surveillance was enhanced with customized queries to identify cases in high-risk counties with reported H5N1 detected in animals. In coordination with VHA clinical laboratories, select samples were sent to PHRL. PHRL subtyped specimens received, which included hospitalized cases. Demographics of influenza A cases in VHA were compared with those residing in high-risk "surveilled" counties (with reported H5N1 detection in animals) and those whose specimens were sent to PHRL for H5 subtyping. RESULTS: From 4/1/2024-5/31/2025, we identified 40,406 positive influenza A VHA cases (12.5% with local subtyping performed), including 5,348 cases from "surveilled" counties. A total of 1,155 specimens were received by PHRL for H5 subtyping and 180 completed WGS. Cases from "surveilled" counties had fewer females, fewer in 50-69 age group and more of Hispanic ethnicity compared to other influenza A cases. No H5N1 was detected. CONCLUSION: We highlight the complexity and resources necessary for epidemiologic and laboratory surveillance of H5N1 within a large, national health system during a recognized panzootic. Additional resources for decentralized influenza A subtyping at local VA clinical laboratories are needed as centralized subtyping and WGS at PHRL was not comprehensive. Although H5 influenza has not yet been observed among Veterans within VHA, the ongoing risk warrants continued vigilance and monitoring.