The pandemic period is made up of one phase, phase 6. In phase 6, there is an increased and sustained transmission of the flu in the general population.
Pandemic Stages: Summary
The distinction between phases 1 and 2 is based on the risk of human infection or disease resulting from circulating strains in animals. The distinction is based on various factors and their relative importance according to current scientific knowledge. Factors may include:
Pathogenicity in animals and humans
Occurrence in domesticated animals and livestock or only in wildlife
Whether the virus is enzootic (animals in a specific region are affected) or epizootic (large numbers of animals are infected with the disease), geographically localized or widespread
Other scientific parameters.
The distinction among phases 3, 4, and 5 is based on an assessment of the risk of a pandemic. Various factors and their relative importance according to current scientific knowledge may be considered. Factors may include:
Rate of transmission
Geographical location and spread
Severity of illness
Presence of genes from human strains (if derived from an animal strain)