• Defined by the World Health Organization to include 6 stages of development. At stage 6, a pandemic is is reached.


A pandemic is the rapid spread of disease to a large population spread across a large region outside of normal local boundaries within a short period of time (1-2 weeks)


Phase I

Phase I is the period before any new infectious subtypes have been detected in animals, a stage that is often missed since new subtypes are occur yearly

Phase II

Phase II begins after the new virus has been shown to infect humans

Phase III

Phase 3 begins when cases of the new virus appear in humans throughout the world for example during H5NI virus, or avian flu, a disease that spread from birds to humans but not from humans to humans. [1]

Phase IV

Phase IV occurs when the virus can easily transmit between humans and results in this results in community-level epidemics

Phase V

Phase V involves disease spread across continents and WHO regions[2] and often is inevitibel until true pandemic is reached.

Phase VI

Phase VI is the definition of a pandemic and requires documentation of the disease in multiple continents or two WHO regions[2]

See Also


  1. WHO H5N1
  2. 2.0 2.1 WHO Disease Regions