An influenza pandemic is a global outbreak of disease that occurs when a new influenza A virus appears in the human population, causes serious human illness, and spreads easily from person to person worldwide. Currently there is no pandemic influenza in the world.

Because people have little or no immune protection from such new viruses, there can be high levels of illness, death, social disruption, and economic loss. The last major flu pandemic occured in 1918 and killed as many as 40 million people worldwide, inlcuding more than 500,000 in the United States.

The H5N1 avian influenza or "bird flu" covered in the news has not qualified as a pandemic strain of influenza and scientists cannot predict if or when this might happen. However, the virus continues to spread in birds and from birds to some people, so public health experts are on high alert.