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Update Summary
May 26, 2023
The following section was updated:
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CHAPTER SUMMARY FROM THE PHARMACOTHERAPY HANDBOOK
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For the Chapter in the Schwinghammer Handbook, please go to Chapter 43, Influenza.
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KEY CONCEPTS
Influenza is a viral illness associated with high mortality and high hospitalization rates among persons older than 65 years. Aging of the population is contributing to an increased disease burden in the United States.
Seasonal influenza epidemics are the result of viral antigenic drift, which is why the influenza vaccine is changed on a yearly basis. Antigenic drift forms the foundation of the recommendation for annual influenza vaccination.
The acquisition of a new hemagglutinin and/or neuraminidase by the influenza virus is called antigenic shift, which results in a novel influenza virus that has the potential to cause a pandemic.
The primary route of influenza transmission is person-to-person via inhalation of respiratory droplets, and transmission can occur for as long as the infected person is shedding virus from the respiratory tract.
Clinical diagnosis of influenza is difficult. Classic signs and symptoms include abrupt onset of fever, muscle pain, headache, malaise, nonproductive cough, sore throat, and rhinitis. These signs and symptoms usually resolve within 1 week of presentation.
In the United States, the primary mechanism of influenza prevention is annual vaccination. Vaccination not only prevents influenza illness and influenza-related hospitalizations and deaths but may also decrease healthcare resource use and the overall cost to society.
The inactivated influenza vaccine (IIV) and the live-attenuated influenza vaccine (LAIV) are commercially available for prevention of seasonal influenza. Both vaccines contain influenza A subtypes H3N2 and H1N1, and influenza B virus, which are initially grown in hens’ eggs.
Antiviral drugs for prophylaxis of influenza should be considered adjuncts to vaccine and are not replacements for annual vaccination.
If used, antiviral drugs should be started within 48 hours of symptom onset to maximize effectiveness.
Neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and cap-dependent endonuclease inhibitor (baloxavir) have activity against both influenza A and influenza B viruses. Although the adamantanes inherently have activity against influenza A H1N1 viruses, they are no longer used clinically due to overwhelming viral resistance.
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BEYOND THE BOOK
Complete the influenza vaccine table
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Influenza causes significant morbidity and mortality, particularly among young children and the elderly. The Centers for Disease Control and Prevention (CDC) estimates that influenza has resulted ...