#USA, Novel #Influenza A Virus #Infections: 1 case of #H5N5 and 1 case of #H1N2v detected (CDC, Nov. 21 '25)

 

{Excerpt}

Novel Influenza A Virus Infections

Two confirmed human infections with novel influenza A viruses were reported to CDC this week. 

One infection with an influenza A(H5N5) virus was reported by the Washington State Department of Health and one infection with an influenza A(H1N2) variant (A(H1N2)v) virus was reported by the Vermont Department of Health.

One infection with an influenza A(H5N5) virus was reported by the Washington State Department of Public Health. 

-- The case occurred in an individual aged ≥18 years. 

-- This individual developed symptoms during the week ending October 25, 2025 (Week 43) and was hospitalized with their illness during the week ending November 8, 2025 (Week 45). 

-- Respiratory specimens collected at the healthcare facility tested positive for influenza A and were presumptive positive for influenza A(H5) at the University of Washington. 

-- The specimens were sent to the Washington State Public Health Laboratory where influenza A(H5) was confirmed using the CDC influenza A(H5) assay. 

-- Sequencing conducted at the University of Washington and at the CDC indicated this was an influenza A(H5N5) virus.

-- The investigation by public health officials identified that the patient kept backyard poultry that had exposure to wild birds. 

-- The patient remains hospitalized. 

-- This is the twelfth confirmed influenza A(H5) case in Washington overall. 

-- Prior confirmed cases in Washington were associated with commercial poultry exposure. 

-- This is the 71st confirmed human case of A(H5) in the United States since early 2024 and the first human case reported in the United States since February 2025.

One infection with an influenza A(H1N2)v virus was reported by the Vermont Department of Health in an individual aged ≥18 years. 

-- The individual developed symptoms and sought healthcare during the week ending October 4, 2025 (Week 40), was hospitalized but discharged on the same day, and has recovered from their illness. 

-- The investigation conducted by state public health officials was unable to determine whether the individual had exposure to swine or other animals, or whether the patient's close contacts exhibited any illness. 

-- No human-to-human transmission has been identified associated with this case.

-- When an influenza virus that normally circulates in swine (but not people) is detected in a person, it is called a “variant” influenza virus. Most human infections with variant influenza viruses occur following exposure to swine, but human-to-human transmission can occur. It is important to note that in most cases, variant influenza viruses have not shown the ability to spread easily and sustainably from person to person.

(...)

Source: 

Link: https://www.cdc.gov/fluview/surveillance/2025-week-46.html

____