#19,385
Just over 2 weeks ago (Oct 8th) USDA/APHIS announced the first detection of H5N1 in dairy cattle in Washington State, which was followed a week later by the first (reportedly mild) human H5N1 infection reported in the U.S. in 2026 (see Washington State Confirms Human Avian Flu Infection).
Since then, we've seen the number of infected dairy herds in Washington state rise to 3, then 8 - and as of yesterday - 9.
Meanwhile, the USDA reports that Texas has detected four infected herds in the past 30 days, and Kansas has reported one. While details on how the HPAI virus was introduced into Washington's dairy herds, how it is spreading, and the genotype have been scant, overnight GISAID announced the Washington human case was B3.13.
Recently, genetic sequence data was released on GISAID from a case of captive American mink and cases of dairy cows from Idaho and Utah from the B3.13 lineage (ggFlu genotype E.2). Some of these sequences presented mutations associated with antigenic drift/escape and mild drug resistance.
On 12 October 2026, the first case of a human H5N1 infection this year was detected in Washington State. The sequence (EPI_ISL_205571770) clusters with recent samples from Idaho and Utah, carrying the same mutation in the NA segment.
Yesterday, the CDC's weekly FluView report noted:
Novel Influenza A Virus Infections
One confirmed human infection with avian influenza A(H5N1) virus was reported to CDC this week. To date, human-to-human transmission of influenza A(H5) virus has not been identified in the United States.
The case was reported by the Washington State Department of Health and occurred in a worker aged ≥18 years at a commercial dairy cattle farm where highly pathogenic avian influenza (HPAI) A(H5N1) virus has been detected in cows. This individual developed eye irritation and upper respiratory symptoms, which they reported to the local health department. Specimens were collected from the individual and tested at the state public health laboratory using the CDC influenza A(H5) assay during the week ending October 17, 2026 (Week 41). Influenza A(H5) virus was confirmed by the state public health laboratory. Additional testing conducted by CDC determined this was an influenza A(H5N1) virus. This is the first influenza A(H5) case associated with a dairy worker in Washington.
While influenza activity in the United States remains low, the FluView report indicates it is rising. Since seasonal influenza continues to evolve, this year's Northern Hemisphere vaccine contains 3 new components (H1N1, H3N2, Influenza B).
A little over a month ago, in Preprint: Near real-time data on the human neutralizing antibody landscape to influenza virus in summer of 2026 shows antigenic advance of H3N2 subclade K region D mutants and H1N1 D.3.1.1 Sa mutants, we looked at some of this ongoing evolution.
Among their findings, the authors identified 72 serum samples in which an H1N1 D.3.1.1 virus carrying G155E was more than twofold less effectively neutralized than a comparable virus without that mutation. Those samples tended to come from teenagers and young adults (roughly 15–25 years old).
While it isn't clear how much - if any - impact this will have on this year's flu vaccine effectiveness, this week's FluView carries the following caveat:
- Since Week 21 (the week ending May 30, 2026), 81.5% of the influenza A viruses reported have been A(H1N1)pdm09 and among these, the majority have been D.3.1.1 HA subclade.
- The A(H1N1) viruses detected this season are still A(H1N1)pdm09 viruses, which emerged in 2009 and have caused seasonal epidemics globally since then. Influenza viruses are constantly changing, usually requiring updates to influenza vaccine viruses each season. Historically, influenza A(H1N1)pdm09 viruses have changed less often than A(H3N2) viruses. Recently circulating influenza A(H1N1)pdm09 viruses (which are in an HA subclade called "D.3.1.1") are dividing into different groups showing different genetic changes. It is too early to know what viruses may predominate or to say whether there might be implications on flu vaccine effectiveness this season.
Last week I reported that the CDC had announced 8 H1N1 viruses tested over the summer showed resistance markers. This week's FluView leaves that number unchanged.
Our last stop is the USDA's poultry HPAI dashboard, which shows an October uptick in both backyard and commercial outbreaks. Although commercial operations see the biggest losses in birds, backyard flocks are more often affected.
While most commercial poultry producers have a good deal of experience in dealing with outbreaks, surveys indicate that backyard producers are generally less well aware of the signs of avian flu, and may be less inclined to wear PPE.
All reasons why I've updated my Flu, COVID, and Pneumovax vaccines, and will happily don an N95 mask in crowded indoor venues.
None of which guarantees I'll come away unscathed this winter, but it certainly increases my chances. And at my age, I'll take any advantage I can get.
