Update: Influenza Activity - United States, October 2-December 17, 2016.

This report summarizes U.S. influenza activity during October 2-December 17, 2016. Influenza activity in the United States remained low in October and has been slowly increasing since November. Influenza A viruses were identified most frequently, with influenza A (H3N2) viruses predominating. Most influenza viruses characterized during this period were genetically or antigenically similar to the reference viruses representing vaccine components recommended for production in the 2016-17 Northern Hemisphere influenza vaccines.