- Influenza is a striking example of a viral disease in which pathogens constantly change and adaptation is of major significance in the appearance of seasonal outbreaks. These, in turn, can become widespread, possibly pandemic. Pandemic influenza differs from seasonal influenza outbreaks essentially by the emergence of a novel strain of the virus that, at times, is also characterized by enhanced pathogenicity and virulence. The last three influenza pandemics have risen from avian influenza strains, although other subtypes are equally capable of producing pandemic strains. For example, the Latest influenza outbreak, which was declared by the World Health Organization as a pandemic, is of swine origin. A severe influenza pandemic may have significant consequences on social and economicaL structures. Therefore, proper prior planning is essential for capabilities built-up to better cope with possibly worse future pandemics. Each influenza pandemic poses a different challenge, but, nevertheless the basic means for response are similar.