Pandemic Stages

In order to classify if a disease outbreak is either an epidemic or a pandemic, the World Health Organization created criteria in order to distinguish the outbreak level. Listed below are the 6 phases of a pandemic as defined by the WHO:


 * Phase 1: There is no animal influenza virus that is circulating among animals that cause infection to humans
 * Phase 2: An animal influenza or virus circulating in wild or domestic animals is known to cause infections in humans and is considered to be a potential pandemic threat
 * Phase 3: An animal or human-animal influenza virus has caused sporadic cases or small clusters of disease in people but has not caused any human-to-human transmission that can sustain a community-level outbreak
 * Phase 4: Human-to-human transmission of the virus is verified to be sustained in community-level outbreaks
 * Phase 5: The same identified outbreak in phase 4 has caused sustained community-level outbreaks in two or more other countries in one WHO region
 * Phase 6: In addition to the criteria in phase 5, the virus has caused community-level outbreaks in at least one other country