Phase-Phase Outbreak Disease Source

Phase 1:
No human infections caused by viruses circulating in animals

Phase 2:
Flu virus in animals to infect humans, and this is a potential pandemic

Phase 3:
Sporadic flu infects humans, but no significant inter-human transmission

Phase 4:
Human to human transmission in a country

Phase 5:
Transmission from humans to humans in two countries. Strong signal that the disease would soon cause a pandemic

Phase 6:
Infectious virus among humans in many countries is called a global pandemic

Post-Peak:
Pandemic activity decreased, although the second wave is still possible

Post-Pandemic:
Activity returned to normal at the level of seasonal flu