- Seasonal Influenza (or common flu) is a respiratory illness that can be transmitted person to person. Most people have some immunity, and a vaccine is available.
- H1N1 Influenza (or swine flu) is a respiratory disease of pigs caused by type A influenza viruses that causes regular outbreaks in pigs. People do not normally get swine flu, but human infections can and do happen. Swine flu viruses have been reported to spread person-to-person, but in the past, this transmission was limited and not sustained.
- Avian Influenza (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 Influenza (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.
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