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Source: Njoku JC. Influenza. In: DiPiro JT, Talbert RL, Yee GC, Matzke GR, Wells BG, Posey LM, eds. Pharmacotherapy: A Pathophysiologic Approach. 10th ed. New York, NY: McGraw-Hill; 2017. Accessed March 25, 2017.


  • Viral illness associated with high mortality and hospitalization rates in persons >65 years, children under 2 years old, and those who have underlying medical conditions.


  • 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 (eg, 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.Comparison of Trivalent (TIV) and Live-Attenuated Influenza Vaccine (LAIV)

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