Seasonal Influenza A(H3N2) Activity and Antiviral Treatment of Patients with Influenza

Effective 2017

The Los Angeles County Health Alert Network warns that influenza activity in Los Angeles County is elevated and increasing. This activity is occurring nationwide, prompting the Centers for Disease Control and Prevention (CDC) to issue a health advisory today: Seasonal Influenza A(H3N2) Activity and Antiviral Treatment of Patients with Influenza.

This CDC advisory provides notice about an increase in influenza activity in recent weeks, its clinical implications, and updated recommendations on influenza antiviral drug treatment.

Influenza A(H3N2) viruses have predominated so far this season. Influenza A(H3N2) viruses are associated with more hospitalizations and more severe illness when compared with illness caused by influenza A(H1N1) viruses. 

The CDC expects that the influenza vaccine could be similarly effective this season compared with last season and emphasizes that antiviral therapy (oseltamivir, zanamivir, and peramivir) are important adjuncts to seasonal influenza vaccination. Antiviral therapy should be considered early in the course of illness for anyone with suspected or confirmed influenza, especially patients who are hospitalized, severely ill, or at high risk for complications.

View the full Seasonal Influenza A(H3N2) Activity and Antiviral Treatment of Patients with Influenza CDC Advisory.

Key Points For Clinicians

This CDC Health Advisory is being issued to:

  • Remind clinicians that influenza should be high on their list of possible diagnoses for ill patients because influenza activity is increasing nationwide; and
  • ​Advise clinicians that all hospitalized patients and all high-risk patients (either hospitalized or outpatient) with suspected influenza should be treated as soon as possible with a neuraminidase inhibitor antiviral. While antiviral drugs work best when treatment is started within 2 days of illness onset, clinical benefit has been observed even when treatment is initiated later.

Key Recommendations:

  • CDC recommends antiviral medications for treatment of influenza as an important adjunct to annual influenza vaccination.
  • All hospitalized, severely ill, and high-risk patients with suspected or confirmed influenza should be treated with antivirals.
  • Clinical benefit is greatest when antiviral treatment is administered as early as possible after illness onset.  Therefore, antiviral treatment should be started as soon as possible after illness onset and should not be delayed even for a few hours to wait for the results of testing. Ideally, treatment should be initiated within 48 hours of symptom onset. However, antiviral treatment initiated later than 48 hours after illness onset can still be beneficial for some patients.
  • CDC offers information to assist clinicians about influenza testing decisions. The most accurate influenza tests are molecular assays. 
  • Neuraminidase inhibitors can benefit other individuals with influenza.