Seasonal (or common) flu– A respiratory illness that can be transmitted person to person. Most people have some immunity, and a vaccine is available.
Avian (or bird) flu – Caused by influenza viruses that occur naturally among wild birds. The H5N1 variant is deadly to domestic fowl and can be transmitted from birds to humans. There is no human immunity and no vaccine is available.
Pandemic flu – Virulent human flu that causes a global outbreak, or pandemic, of serious illness. Because there is little natural immunity, the disease can spread easily from person to person. Currently, there is no pandemic flu.
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 from person to person, causes serious illness, and can sweep across the country and around the world in very short time.
It’s difficult to predict when the next flu pandemic will occur or how severe it will be. Wherever and whenever a pandemic starts, everyone around the world is at risk. Countries may close their borders and restrict travel to delay arrival of the virus, but such measures cannot stop it.
Health professionals are concerned that the current continued spread of a highly pathogenic avian H5N1 virus across eastern Asia represents a significant threat to human health. The H5N1 virus has raised concerns about a potential human pandemic because:
- It is especially virulent
- It is being spread by migratory birds
- It can be transmitted from birds to mammals and in some circumstances to humans, and
- Like other influenza viruses, it continues to evolve.
Since 2003, a growing number of human H5N1 cases have been reported in Azerbaijan, Cambodia, China, Djibouti, Egypt, Indonesia, Iraq, Thailand, Turkey, and Vietnam. More than half of the infected people died. Most of these cases are believed to have been caused by exposure to infected poultry. There has been no sustained human-to-human transmission of the disease, but the concern is that H5N1 will evolve into a virus capable of human-to-human transmission.