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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 very short time.
It is difficult to predict when the next influenza pandemic will occur or how severe it will be. Wherever and whenever a pandemic starts, everyone around the world is at risk. Countries might, through measures such as border closures and travel restrictions, delay arrival of the virus, but cannot stop it.
Health professionals are concerned that the continued and expanded spread of a highly pathogenic-and now endemic-avian H5N1 virus across eastern Asia and other countries represents a significant threat. The H5N1 virus has raised concerns about a potential human pandemic because:
Since 2003, a growing number of human H5N1 cases have been reported in Cambodia, China, Indonesia, Iraq, Thailand, Turkey, and Vietnam, and more than half of the people infected with the H5N1 virus have died. These cases are all believed to have been caused by exposure to infected poultry. The concern is that H5N1 will evolve into a virus capable of human to human transmission.