Definition of a Pandemic
The emergence of influenza A virus significant different genetically from circulating human influenza A viruses (i.e. many or most of the population are non-immune to the new virus) with the following three characteristics: able to infect humans, able to cause disease in humans, able to spread from human to human quite easily
WHO pandemic phases
Pandemic phase one: No animal influenza virus circulating among animals has been reported to cause infection in humans. Pandemic phase two: An animal influenza virus circulating in domesticated or wild animals is known to have caused infection in humans and is therefore considered a specific potential pandemic threat.
Pandemics of the 20th Century
1918 - 1919 Spanish Influenza, 1957 - 1958 Asian Flu, 1968 - 1969 Hong Kong Flu.
Q&A on influenza pandemics
What is influenza? What is a pandemic? What happens during a pandemic – how many people are affected?