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Definition of Terms (World Health Organization)
Definition of Terms - WHO
Interpandemic phase:
The period between influenza pandemics.
Alert phase:
This is the phase when influenza caused by a new subtype has been identified in humans. Increased vigilance and careful risk assessment, at local, national and global levels, are characteristic of this phase.
Pandemic phase:
This is the period of global spread of human influenza caused by a new subtype based on global surveillance.
Transition phase:
As the assessed global risk reduces, de-escalation of global actions may occur, and reduction in response activities or movement towards recovery actions by countries may be appropriate, according to their own risk assessments