The World Health Organization (WHO) predicted a pandemic influenza outbreak sometime this century. Pandemic influenza occurs when a new flu virus infection breaks out worldwide, spreading rapidly from one country to another. Infectious diseases can spread around the globe in a matter of hours in today’s world of airline travel.

There were three other influenza pandemics in the 20th century: 1918, 1957 and 1968.

Influenza is an infection of the lungs and airways caused by a virus. Each year, various types of influenza circulate throughout the world. These viruses are constantly changing, producing new strains. Usually an individual’s previous bout of influenza offers some protection against infections caused by similar strains of flu virus. Pandemics occur when the flu virus changes so drastically that most people have no immunity to it and infection spreads rapidly from country to country.

The WHO has declared the H1N1 Influenza A virus to be a global influenza pandemic. At this time, WHO considers the overall severity of the influenza pandemic to be moderate. This assessment is based on scientific evidence available to WHO, as well as input from its Member States on the pandemic's impact on their health systems, and their social and economic functioning.

The moderate assessment reflects that:

• Most people recover from infection without the need for hospitalization or medical care.
• Overall, national levels of severe illness from influenza A(H1N1) appear similar to levels seen during local seasonal influenza periods, although high levels of disease have occurred in some local areas and institutions.
• Overall, hospitals and health care systems in most countries have been able to cope with the numbers of people seeking care, although some facilities and systems have been stressed in some localities.

WHO is concerned about current patterns of serious cases and deaths that are occurring primarily among young persons, including the previously healthy and those with pre-existing medical conditions or pregnancy.

Large outbreaks of disease have not yet been reported in many countries, and the full clinical spectrum of disease is not yet known.

Some information for this site was taken from: The World Health Organization Pandemic preparedness page.