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Source: Njoku JC and Hermsen ED. Influenza. In: DiPiro, JT, Talbert RL, Yee GC, Matzke GR, Wells BG, Posey LM. Pharmacotherapy: A Pathophysiologic Approach. 8th ed. Accessed June 26, 2012.

  • Viral illness associated with high mortality and hospitalization rates in persons >65 years.

  • Transmitted person to person via inhalation of respiratory droplets

  • Hemagglutinin allows virus to enter host cells.
  • Incubation period: 1–7 days (average 2 days)
    • Children infectious for longer period of time than adults.
    • Viral shedding persists for weeks to months if immunocompromised.
  • Immunity occurs through antibody development directed at surface antigens, particularly hemagglutinin.
    • Immunity to one subtype does not confer protection against other subtypes or types.

  • Seasonal epidemics result in 25–50 million cases, ~200,000 hospitalizations, and >30,000 deaths each year in the United States.
    • Overall, more people die of influenza than of any other vaccine-preventable illness.
    • Deaths often result from:
      • Secondary bacterial pneumonia
      • Primary viral pneumonia
      • Exacerbations of underlying comorbidities
  • Types A, B, and C affect many species.
    • A and B viruses cause disease in humans.

  • Primary prevention
    • Vaccination primary means of influenza prevention.
    • Infection control measures to limit spread of influenza
      • Hand hygiene
      • Basic respiratory etiquette (cover your mouth when coughing and throw soiled tissues away)
      • Contact avoidance
    • Annual vaccination recommended for all persons age 6 months or older.
    • Two vaccines currently available (Tables 1 and 2)
      • Trivalent influenza vaccine (TIV)
        • Intramuscular product approved for use in persons age 6 months or older
      • Live-attenuated influenza vaccine (LAIV)
        • Intranasal product approved for use in healthy people 2–49 years of age
        • Not indicated for use in pregnant women or immunocompromised person.
        • Administer 48 hours after completion of influenza antiviral therapy.
        • Administer antiviral therapy 2 weeks after administration of LAIV.
      • Specific strains included in vaccine change each year based on antigenic drift.
  • Postexposure prophylaxis
    • Antiviral drugs available for prophylaxis not replacements for annual vaccination (Table 3).
    • Consider prophylaxis for persons at high risk of serious illness and/or complications who:
      • Cannot be vaccinated
      • Are vaccinated after influenza activity has begun in their community because development of sufficient antibody titers after vaccination takes ~2 weeks
      • Are unvaccinated and have frequent contact with those at high risk
      • Have an inadequate response to vaccination (e.g., advanced HIV disease)
      • Reside in long-term care facility during influenza outbreak (regardless of vaccination status)
      • Are unvaccinated and household contacts of someone diagnosed with influenza

Table 1. Approved Influenza Vaccines for Different Age Groups—United States, 2010–2011 Season

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