Influenza A(H5N5) Virus in Humans

On 15 November 2025, the WHO was notified of a confirmed human infection with influenza A(H5N5) in the United States of America. Influenza A(H5N5) viruses have been detected in North America in wild birds and wild mammals since at least 2023[1]. This is the very first laboratory-confirmed human infection with an influenza A(H5N5) virus in the United States of America and reported globally.

Previously, infections with Influenza A(H5Nx) were reported in the US, but this is the first in the country since February 2025 and the 71st since early 2024. On 20 November, CDC laboratory sequencing verified the virus as influenza A(H5N5), representing the very first human case of this subtype reported globally. The patient was an adult with underlying medical conditions residing in Washington State. The patient developed symptoms including fever during the week ending 25 October 2025. During the week ending 8 November 2025, the patient was hospitalized with a serious illness, and subsequently died on 21 November 2025.

Public health investigation revealed that the patient kept backyard poultry and domestic birds. Additional epidemiological investigations are under way.

The investigation by health authorities in the US is ongoing. Contact tracing identified no further cases amongst contacts, and there is currently no evidence of human-to-human transmission. Due to the constantly evolving nature of influenza viruses, the WHO continues to stress the importance of global surveillance to detect and monitor virological (including genomics), epidemiological and clinical changes associated with emerging or circulating influenza viruses that may affect human health and timely virus sharing for risk assessment.

This case shows that we will never be truly safe. It goes without saying that the currently used Influenza vaccine does not deliver protection for this emerging virus.

[1] Centers for Disease Control and Prevention (CDC). Weekly US Influenza Surveillance Report: Key Updates for Week 46, ending November 15, 2025. See here.