What is an influenza pandemic?

An influenza (flu) pandemic is a worldwide outbreak of flu disease that occurs when a new type of influenza virus appears that people haven't been exposed to before (or haven't been exposed to in a long time). The pandemic virus can cause serious illness because people don't have immunity to the new virus.

The current influenza causing concern around the world as a potential pandemic is swine influenza.

Pandemics are different from seasonal outbreaks of influenza that we see every year. Seasonal influenza is caused by influenza virus types that people have already been exposed to. Its impact on society is less severe than a pandemic, and influenza vaccines (flu shots and nasal spray vaccines) are available to help prevent widespread illness from seasonal flu.

Influenza pandemics are different from many of the other major public health and health care threats facing our country and the world. A pandemic will last much longer than most flu outbreaks and may include 'waves' of influenza activity that last 6 – 8 weeks, separated by months between each outbreak. The number of health care workers able to work may be reduced. Public health officials will not know how severe a pandemic will be until it begins.