Seasonal Influenza A(H3N2) Activity and Antiviral Treatment of
Patients with Influenza
The Centers for Disease Control and Prevention (CDC) is providing:
- a notice about increased influenza A(H3N2) activity and its clinical implications;
- a summary of influenza antiviral drug treatment recommendations;
- an update about approved treatment drugs and supply this season; and
- background information for patients about influenza treatment.
In the United States (U.S.), influenza activity has increased significantly over recent weeks with influenza A(H3N2) viruses predominating so far this season. In the past, A(H3N2) virus-predominant influenza seasons have been associated with more hospitalizations and deaths in persons aged 65 years and older and young children compared to other age groups. In addition, influenza vaccine effectiveness (VE) in general has been lower against A(H3N2) viruses than against influenza A(H1N1)pdm09 or influenza B
Last season, VE against circulating influenza A(H3N2) viruses was estimated to be 32% in the U.S. CDC expects that VE could be similar this season, should the same A(H3N2) viruses continue to predominate. For this reason, in addition to influenza vaccination for prevention of influenza, the use of
antiviral medications for treatment of influenza becomes even more important than usual. The neuraminidase inhibitor (NAI) antiviral medications are most effective in treating influenza and reducing complications when treatment is started early. Evidence from previous influenza seasons suggests that
NAI antivirals are underutilized in outpatients and hospitalized patients with influenza who are recommended for treatment.
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.