This site, like many others, uses small files called cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we'll assume that you are happy to receive all cookies on this website (Cookie Policy). However, if you would like to, you can change your cookie settings at any time.

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