What Is Pandemic Flu?
A pandemic is a global disease outbreak. An influenza pandemic occurs when a new influenza A virus emerges for which there is little or no immunity in the human population, begins to cause serious illness, and then spreads easily person-to-person worldwide.New influenza viruses emerge as a result of a process called antigenic shift, which causes a sudden and major change in influenza A viruses. These changes occur when proteins on the surface of the virus combine in new ways as a result of mutation or exchange of genetic material between multiple influenza viruses. If such changes result in a new influenza A virus subtype that can infect humans and spread easily from person to person, an influenza pandemic can occur.
