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

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 viruses. 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.


CDC guidance about antiviral treatment and prophylaxis for influenza can be found here.

CDC guidance about flu diagnosis can be found here.

The recently redesigned MDPH Flu website  has information for providers and the general public. Click on ‘Information for Healthcare and Public Health Professionals’ for such provider resources as influenza control guidance, model standing orders, screening forms and planning clinics and campaigns.

Click here for the CDC Health Advisory on  Seasonal Influenza A(H3N2) Activity and Antiviral Treatment of Patients with Influenza