A pandemic is a global disease outbreak. An influenza pandemic occurs when a new Influenza A virus emerges for which there is little or no immunity in the human population, begins to cause serious illness, and then spreads easily person-to-person worldwide.

Many scientists believe it is a matter of time until the next influenza pandemic occurs. However, the timing and severity of the next pandemic cannot be predicted. Influenza pandemics occurred three times in the past century - in 1918-1919, 1957-58, and 1968-1969.

Pandemic Alert Phases

The World Health Organization (WHO) has developed an alert system to help inform the world about the seriousness of a pandemic. The alert system has six phases, with Phase 1 having the lowest risk of human cases and Phase 6 posing the greatest risk of a pandemic. Due to the H1N1 virus (or "swine flu") the world is presently in Phase 6 of the pandemic alert.