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Increasing Seasonal Influenza A

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Increasing Seasonal Influenza A (H3N2) Activity Nationally, Especially Among Young Adults and in College and University Settings

Health Advisory

November 24, 2021

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  • Be aware of increasing influenza A (H3N2) activity nationally that could mark the beginning of the 2021-2022 flu season.
  • Recommend and offer the seasonal flu vaccine to all eligible persons aged six months and older.
    • Flu vaccine and COVID-19 vaccine can be given at the same visit.

  • Counsel your patients to use everyday preventive actions in addition to getting a flu vaccine.
    • Includes staying home when sick, covering coughs and sneezes, and washing hands often.

  • Consider testing for both flu and SARS-CoV-2 in patients with influenza-like illness (ILI).

  • Be aware that antiviral treatment is recommended as early as possible for any patient with confirmed or suspected flu who is: a) hospitalized; b) at higher risk for flu complications; or c) developing progressive illness.
    • In patients with suspected flu, decisions about starting antiviral treatment should not wait for laboratory confirmation, however COVID-19 should be excluded if a rapid assay is available.

  • Consider mitigation measures including antiviral post-exposure prophylaxis during flu outbreaks in institutions (e.g., long-term care facilities, university dormitories) in the setting of co-circulation of SARS-CoV-2.

  • Report flu deaths and outbreaks to Public Health – Seattle & King County at (206) 296-4774.

CDC is reporting a recent increase of influenza A (H3N2) in many places in the United States, with most of these infections occurring in young adults. CDC also is aware of flu outbreaks in colleges and universities in several states. Influenza A (H3N2) predominant seasons often are also associated with more severe flu seasons, especially for older adults and young children. Flu vaccination coverage is low nationally and there is still time this season to benefit from getting an annual flu vaccine. Pediatric flu vaccinations in WA are down about 25% from this time last year.

In King County, flu activity remains low. The percent of ILI emergency department (ED) visits seems to be increasing, and this is likely due to increases in ILI ED visits in children < 5 years old (which may be at least partially attributed to higher levels of RSV circulating currently).

Factors known to increase a person's risk of getting serious complications from flu include:

  • Adults 65 years and older
  • Children younger than 5 years (particularly younger than 2 years)
  • People with any of the following:
    • Asthma
    • Neurologic and neurodevelopmental conditions
    • Blood disorders (e.g., sickle cell disease)
    • Chronic lung disease (e.g., chronic obstructive pulmonary disease [COPD], cystic fibrosis)
    • Endocrine disorders (e.g., diabetes mellitus)
    • Heart disease (e.g., congenital heart disease, congestive heart failure, coronary artery disease)
    • Kidney diseases
    • Liver disorders
    • Metabolic disorders (e.g., inherited metabolic disorders and mitochondrial disorders)
    • Immunosuppression due to disease (e.g., HIV or AIDS, or some cancers such as leukemia) or medications (e.g., those receiving chemotherapy or radiation treatment for cancer, or persons with chronic conditions requiring chronic corticosteroids or other drugs that suppress the immune system)
  • People who are obese with a body mass index [BMI] of 40 or higher
  • People younger than 19 years old on long-term aspirin- or salicylate-containing medications.
  • People who have had a stroke

Other people at higher risk from flu:

  • Pregnant people and people up to 2 weeks after the end of pregnancy
  • People who live in nursing homes and other long-term care facilities
  • People from certain racial and ethnic minority groups are at increased risk for hospitalization with flu, including non-Hispanic Black persons, Hispanic or Latinx persons, and American Indian or Alaska Native persons
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