There is a growing fear within the medical community concerning the potential re-occurance of a pandemic influenza outbreak, similar to the 1918 “Spanish flu” pandemic. A pandemic can start when a new influenza virus subtype emerges that meets three conditions: it infects humans causing serious illness; it spreads easily; and there is sustained human-to-human transmission of the virus. The H5N1 virus meets the first two conditions, and the risk that the virus acquires the third ability will persist as long as opportunities for human infections occur.

Vaccines effective against a pandemic virus are not yet available. Although vaccines against H5N1 virus are under development, no vaccine is ready for commercial production and no vaccines are expected to be available until several months after the start of a pandemic. Clinical data on the use of anti-viral drugs to treat H5N1 virus infections is limited at this time.

Avian influenza is an infection caused by avian, or bird, influenza viruses that occur naturally among wild birds. It is usually very contagious among birds and can make some domestic poultry (chickens, ducks or turkeys) very sick and potentially kill them. Although uncommon, infections with these viruses can occur in humans. Of the hundreds of strains of avian influenza A viruses, only four are known to have caused human infections: H5N1, H7N3, H7N7, and H9N2. Since 1997, more than 230 confirmed cases of human infection with avian influenza strains, principally the influenza A virus H5N1, have been reported resulting in death in more than 50% of those infected. Most cases have occured from close contact with infected poultry or with secretions or excretions from infected birds. The spread of avian influenza viruses from person to person has been reported very rarely.