Influenza Virus

Clinical Overview of Influenza

  • Influenza is a serious, contagious respiratory illness that affects 5 to 20 percent of the United States population every year2
  • Every year, seasonal flu is responsible for approximately 36,000 deaths and 226,000 hospitalizations in the U.S. More about the impact of influenza3
  • Influenza A and B viruses are the two types that cause epidemic disease 3
  • New variants of the influenza virus emerge regularly due to mutations that occur during viral replication3

Signs and Symptoms

  • Influenza is spread from person to person through respiratory droplets that are dispersed when an infected person coughs or sneezes in close proximity to someone who is not infected
  • The typical incubation period is 1 to 4 days, with an average of 2 days
  • Adults can be infectious from 1 day before onset of symptoms to 5 days after illness onset
  • Children can be infectious for 10 days or more after onset of symptoms, and young children can shed the virus before their illness onset
  • Uncomplicated influenza is characterized by abrupt onset of signs and symptoms that can include:
    • Fever
    • Chills
    • Myalgia
    • Headache
    • Tiredness
    • Non-productive cough
    • Sore throat
    • Rhinitis
  • Uncomplicated influenza typically resolves within 1 week, although cough and malaise can persist for up to 2 weeks 3

Complications

Complications of influenza can include:

  • Bacterial pneumonia
  • Ear infections
  • Sinus infections
  • Dehydration
  • Worsening of chronic medical conditions such as congestive heart failure, asthma or diabetes 2

Populations at Increased Risk

Patients at high risk for influenza-related complications and severe disease include:

  • Pediatric patients aged 6 to 59 months
  • Pregnant women
  • Patients aged 50 years and older
  • Patients of any age with chronic medical conditions
  • Patients who live with or care for persons at high risk such as household contacts and healthcare workers 3

Learn about TAMIFLU for influenza treatment and influenza prevention.

Influenza Resources

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Important Safety Information

Indications

TAMIFLU is indicated for the treatment of uncomplicated influenza caused by viruses types A and B in patients 1 year and older who have been symptomatic for no more than 2 days.

TAMIFLU is also indicated for the prophylaxis of influenza in patients 1 year and older.

Efficacy of TAMIFLU in patients who begin treatment after 48 hours of symptoms has not been established.

TAMIFLU is not a substitute for early and annual vaccination as recommended by the Centers for Disease Control's Advisory Committee on Immunization Practices (ACIP).

There is no evidence for efficacy of TAMIFLU in any illness caused by agents other than influenza viruses Types A and B.

Influenza viruses change over time. Emergence of resistance mutations could decrease drug effectiveness. Other factors (for example, changes in viral virulence) might also diminish clinical benefits of antiviral drugs. Prescribers should consider available information on influenza drug susceptibility patterns and treatment effects when deciding whether to use TAMIFLU.

Safety Information

TAMIFLU is contraindicated in patients who have had severe allergic reactions such as anaphylaxis or serious skin reactions such as toxic epidermal necrolysis, Stevens-Johnson syndrome, or erythema multiforme to any component of TAMIFLU.

In postmarketing experience, rare cases of anaphylaxis and serious skin reactions, including toxic epidermal necrolysis, Stevens-Johnson syndrome and erythema multiforme, have been reported with TAMIFLU. Tamiflu should be stopped and appropriate treatment instituted if an allergic-like reaction occurs or is suspected.

Influenza can be associated with a variety of neurologic and behavioral symptoms, which can include events such as hallucinations, delirium and abnormal behavior, in some cases resulting in fatal outcomes. These events may occur in the setting of encephalitis or encephalopathy but can occur without obvious severe disease. There have been postmarketing reports (mostly from Japan) of delirium and abnormal behavior leading to injury, and in some cases resulting in fatal outcomes, in patients with influenza who were receiving TAMIFLU. Because these events were reported voluntarily during clinical practice, estimates of frequency cannot be made but they appear to be uncommon based on TAMIFLU usage data. These events were reported primarily among pediatric patients and often had an abrupt onset and rapid resolution. The contribution of TAMIFLU to these events has not been established. Patients with influenza should be closely monitored for signs of abnormal behavior. If neuropsychiatric symptoms occur, the risks and benefits of continuing treatment should be evaluated for each patient.

Serious bacterial infections may begin with influenza-like symptoms or may co-exist with or occur as complications during the course of influenza. TAMIFLU has not been shown to prevent such complications.

Treatment efficacy in subjects with chronic cardiac and/or respiratory disease has not been established. No difference in the incidence of complications was observed between the treatment and placebo groups in this population.

No information is available regarding treatment of influenza in patients at imminent risk of requiring hospitalization.

Efficacy of TAMIFLU has not been established in immunocompromised patients.

The concurrent use of TAMIFLU with live attenuated influenza vaccine (LAIV) intranasal has not been evaluated. However, because of the potential for interference between these products, LAIV should not be administered within 2 weeks before or 48 hours after administration of TAMIFLU, unless medically indicated.

Adverse events that occurred more frequently in patients treated with TAMIFLU than in patients taking placebo and occurred in ≥2% of patients were (TAMIFLU%, placebo%):

  • Treatment in adults – nausea (10%, 6%), vomiting (9%, 3%), bronchitis (2%, 2%)
  • Treatment in pediatrics – vomiting (15%, 9%), abdominal pain (5%, 4%), epistaxis (3%, 3%), ear disorder (2%, 1%)
  • Prophylaxis of adults – headache (18%, 18%), nausea (7%, 3%), diarrhea (3%, 2%), vomiting (2%, 1%), abdominal pain (2%, 1%)
  • Prophylaxis of pediatrics – vomiting (10%, 2%), abdominal pain (3%, 0%), nausea (4%, 1%)
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