The burial of plague victims 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 (like a continent), or even worldwide.
The agent that causes the disease 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 causes many deaths, but it is not a pandemic because it is usually not infectious.
World Health Organization pandemic phases
The World Health Organization (WHO) has developed a plan to prepare the global fight against influenza. It defines the stages of a pandemic and makes recommendations about what countries should do 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. However, a variant of the virus causes disease in animals. This means there is a threat of human disease.
Pandemic alert period:
Phase 3: Humans get infected with a new subtype of the flu virus. However, the virus is not spreading from person to person.
Phase 4: There are small cluster(s) of flu infection. Person-to-person spread is limited and localized.
Phase 5: There are larger cluster(s) of flu infection. Person-to-person spread is still localized.
Pandemic period:
Phase 6: Pandemic: The flu has spread throughout the general population. Person-to-person spread is increased and sustained..
