{Extract, Summary}
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Key Points
° Multiple seasonal influenza surveillance indicators continue to increase in many parts of the country.
° This early-season influenza activity is currently higher than typically observed at this time of year, but an earlier increase in activity does not necessarily lead to a higher seasonal peak or greater overall severity.
° During Week 43 (the week ending October 31, 2026), of the 513 influenza viruses reported by public health laboratories, 502 were influenza A and 11 were influenza B. Of the 388 influenza A viruses subtyped during Week 43, 379 (97.7%) were influenza A(H1N1)pdm09, 7 (1.8%) were A(H3N2) and 2 (0.5%) were influenza A(H5).
° Since Week 21 (the week ending May 30, 2026), 83.4% 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 influenza 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, often 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") have divided into distinct groups with different genetic changes in their HA genes. We are seeing more genetic diversity among co-circulating A(H1N1)pdm09 viruses than we have before.
° It is too early to know what viruses may predominate or to say whether there might be implications on flu vaccine effectiveness this season.
° Two pediatric deaths associated with season influenza virus infection and occurring during the 2026-27 influenza season were reported to CDC this week.
° Because case investigation takes time, flu-associated deaths in children may be reported to CDC weeks after they occur; counts are preliminary and may increase. All reported cases meet the influenza-associated pediatric mortality case definition.
° The preliminary in-season severity assessment has classified the severity of influenza activity at this point in the season as low across all ages and for children (0-17years), adults (18-64 years) and older adults (65+ years). The severity assessment for the season may change as flu activity is currently increasing.
° CDC estimates that there have been at least 1,700,000 illnesses, 25,000 hospitalizations, and 1,400 deaths from flu so far this season.
° CDC’s FluSight forecasts predict a likely increase nationally in both flu hospital admissions and the percentage of emergency department visits due to flu for the week ending November 21. The number of new flu hospital admissions is forecast to range from 6,900 to 30,100 admissions, while the national percentage of emergency department visits due to flu is forecast to range from 1.6% to 6.7%.
° Annual seasonal influenza (flu) vaccination is recommended. Influenza vaccines are available for persons aged 6 months and older. People who are recommended for influenza vaccination but have not been vaccinated yet this season are encouraged to be vaccinated now.
° There are prescription flu antiviral drugs that can treat flu illness; those should be started as early as possible and are especially important for patients at higher risk for influenza complications.1
° Two confirmed cases of avian influenza A(H5) virus infection were reported to CDC this week, including one death. To date, human-to-human transmission of avian influenza A(H5) virus (H5 bird flu) has not been identified in the United States.
° Influenza viruses are among several viruses contributing to respiratory disease activity. CDC is providing updated, integrated information about COVID-19, flu, and respiratory syncytial virus (RSV) activity on a weekly basis.
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Novel Influenza A Virus Infections
° Two confirmed human infections with avian influenza A(H5) virus were reported to CDC this week, including one death. To date, human-to-human transmission of avian influenza A(H5) virus has not been identified in the United States.
° Both cases were reported by the Washington State Department of Health and occurred in adults aged ≥18 years who worked at commercial dairy cattle farms where highly pathogenic avian influenza (HPAI) A(H5N1) virus has been detected in cows.
° One individual developed respiratory symptoms during the week ending October 24, 2026 (Week 42). The patient presented to an emergency department the following week, was hospitalized, and has died. A respiratory specimen collected at the healthcare facility tested positive for influenza A and was presumptive positive for influenza A(H5) at the University of Washington. The specimen was sent to the Washington State Public Health Laboratory where influenza A(H5) was confirmed using the CDC influenza A(H5) assay. Additional testing conducted by the University of Washington determined this was an avian influenza A(H5N1) virus.
° The second individual developed conjunctivitis and sought healthcare. 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 31, 2026 (Week 43). Influenza A(H5) virus was confirmed by the state public health laboratory. The specimen has been shipped to CDC for additional testing.
° There has been a total of three influenza A(H5) cases in dairy workers in Washington.
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Source: US Centers for Disease Control and Prevention, https://www.cdc.gov/fluview/surveillance/2026-week-43.html
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