Update: influenza activity--United States, October 2-November 26, 2011.

During October 2-November 26, 2011, influenza activity remained low in the United States. Thus far, influenza A viruses have predominated, and the majority are antigenically related to the 2011-12 influenza vaccine strains for the Northern Hemisphere. This report summarizes U.S. influenza activity since October 2 and updates the previous summary.