The burial of the victims of the plague in Tournai. Fragment of a miniature from "The Chronicles of Gilles Li Muisis" (1272-1352), abbot of the monastery of St. Martin of the Righteous. Bibliothèque royale de Belgique, MS 13076-77, f. 24v.

A pandemic (from Greek παν pan all + δήμος demos people) is an epidemic (an outbreak of an infectious disease) that spreads across a large region (for example a continent), or even worldwide.

Common killers and pandemics

According to the World Health Organization, a pandemic can start when three conditions have been met:

  • the emergence of a disease new to the population.
  • the agent infects humans, causing serious illness.
  • the agent spreads easily and sustainably among humans.

A disease or condition is not a pandemic merely because it is widespread or kills many people; it must also be infectious. For example cancer is responsible for many deaths but is not considered a pandemic because the disease is not infectious (although certain causes of some types of cancer might be).

World Health Organization pandemic phases

The World Health Organization (WHO) has developed a plan to prepare globally the fight against influenza. It defines the stages of a pandemic and makes recommendations for national measures before and during a pandemic. The phases are:

Interpandemic period:

  • Phase 1: No new influenza virus subtypes have been detected in humans.
  • Phase 2: No new influenza virus subtypes have been detected in humans, but an animal variant threatens human disease.

Pandemic alert period:

  • Phase 3: Human infection(s) with a new subtype but no human-to-human spread.
  • Phase 4: Small cluster(s) with limited localized human-to-human transmission
  • Phase 5: Larger cluster(s) but human-to-human spread still localized.

Pandemic period:

  • Phase 6: Pandemic: increased and sustained transmission in general population.

Related pages


  • Steward's "The Next Global Threat: Pandemic Influenza".

Other websites