Update: Influenza activity--United States and worldwide, June-September, 2002.

During June-September 2002, influenza A (H3N2) and B viruses circulated worldwide and were associated with mild to moderate levels of disease activity. Influenza B viruses predominated in Africa, and both influenza A (H3N2) and B viruses circulated widely in Asia, Oceania, and Latin America, except in Chile and Taiwan, where A (H1) viruses predominated. In North America, sporadic isolates of influenza A (H3N2), A (H1), and B viruses were identified. This report summarizes influenza activity in the United States and worldwide during June-September 2002. Influenza activity in North America typically peaks during December-March, which underscores the need to begin vaccinating against influenza in October and to continue vaccination into December and throughout the influenza season.