Seasonal (or common) flu
is a respiratory illness that can be transmitted person to person. Most people
have some immunity, and a vaccine is available.
Avian (or bird) flu
is 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 is
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.