Update: influenza activity--United States and worldwide, 1997-98 season, and composition of the 1998-99 influenza vaccine.

In collaboration with the World Health Organization (WHO), the WHO international network of collaborating laboratories, and state and local health departments, CDC conducts surveillance to monitor influenza activity and to detect antigenic changes in the circulating strains of influenza viruses. This report summarizes surveillance for influenza in the United States and worldwide during the 1997-98 influenza season and describes the composition of the 1998-99 influenza vaccine.