Update: Influenza activity--United States, 2002-03 season

Area of Science:

• Epidemiology
• Public Health
• Virology

Background:

• Influenza activity in the United States remained low during the initial period of surveillance.
• Influenza surveillance data were collected from late September 2002 through early January 2003.
• Anticipation of increased influenza cases in the upcoming weeks was noted.

Purpose of the Study:

• To summarize influenza activity in the United States.
• To provide an update on the influenza situation for the 2002-2003 season.
• To report on the antigenic match between circulating influenza viruses and the seasonal vaccine.

Main Methods:

• Surveillance of laboratory-confirmed influenza infections across 25 states.
• Isolation and antigenic characterization of influenza viruses.
• Summary and analysis of influenza activity data.

Main Results:

• Overall influenza activity was low during the specified period.
• Laboratory-confirmed influenza cases were reported from 25 states.
• Circulating influenza viruses were antigenically well-matched to the seasonal influenza vaccine.

Conclusions:

• Influenza activity is expected to increase in the coming weeks.
• The current influenza vaccine is likely to be effective against circulating strains.
• Continued monitoring of influenza activity is essential.