During the 2012–13 influenza season in the United States, influenza activity increased through November and December before peaking in late December. Influenza A (H3N2) viruses predominated overall, but influenza B viruses and, to a lesser extent, 2009 influenza A (H1N1) (2009 H1N1) viruses also were reported in the United States. This influenza season was moderately severe, with a higher percentage of outpatient visits for influenza-like illness (ILI), higher rates of hospitalization, and more reported deaths attributed to pneumonia and influenza compared with recent years.

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Stephen B. Thacker CDC Library collection

United States