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A pandemic is a global disease outbreak. A flu pandemic occurs when a new influenza virus emerges for which people have little or no immunity and for which there is no vaccine. The disease spreads easily person-to-person, causes serious illness, and can sweep across the country and around the world in a very short time.
It is difficult to predict when the next influenza pandemic will occur or how severe it will be. In the past century pandemics occurred in 1918-1919, 1957-1958 and 1968-1969.
Wherever and whenever a pandemic starts, everyone around the world is at risk. Countries might delay arrival of the virus, through measures such as border closures and travel restrictions, but they cannot stop it.
Avian (bird) flu is caused by influenza A avian viruses that occur naturally among birds. There are many different subtypes of type A influenza viruses. All known subtypes can be found in birds. The avian flu currently of concern is the H5N1 subtype. Avian H5N1 flu in humans is currently very limited and not a pandemic.
Although H5N1 probably poses the greatest current pandemic threat, other avian influenza A subtypes also have infected people in recent years. For example, in 1999, H9N2 infections were identified in Hong Kong; in 2002; and 2003, H7N7 infections occurred in the Netherlands and H7N3 infections occurred in Canada. These viruses also have the potential to give rise to the next pandemic.
For more information on pandemic or avian flu, go to www.pandemicflu.gov.
Source: U.S. Department of Health and Human Services