The official flu season runs late September to mid May. 

The Department for Public Health publishes reports weekly​​​​​​​​​​​​​​​​ throughout the flu season.

The flu activity level is submitted by the Department for Public Health to the Centers for Disease Control and Prevention weekly as part of the national flu surveillance system.

The possible flu activity levels and their definitions are:

• No Activity: No laboratory-confirmed cases of influenza and no reported increase in the number of cases of influenza-like illness (ILI).
• Sporadic: Small numbers of laboratory-confirmed influenza cases or a single laboratory-confirmed influenza outbreak has been reported, but there is no increase in cases of ILI.
• Local: Outbreaks of influenza or increases in ILI cases and recent laboratory-confirmed influenza in a single region of the state.
• Regional: Outbreaks of influenza or increases in ILI and recent laboratory confirmed influenza in at least two but less than half the regions of the state with recent laboratory evidence of influenza in those regions.
• Widespread: Outbreaks of influenza or increases in ILI cases and recent laboratory-confirmed influenza in at least half the regions of the state with recent laboratory evidence of influenza in the state.

View the Influenza Sentinel Surveillance Site fact sheet.