The World Health Organization (WHO) declared the outbreak of the H1N1 influenza virus a pandemic - obviously bad news for us fragile humans.

The announcement made yesterday warns the WHO's 194 member nations to prepare for the new flu strain, which could infect as much as a third of the population in the first wave and later return more severely.

"The world is moving into the early days of its first influenza pandemic of the 21st century," WHO's director general Margaret Chan said. "We anticipate this action will raise many questions and that often these questions do not have simple answers."

WHO is now advising authorities around the world to "quickly prepare commercial-scale pandemic vaccine of this H1N1 virus".

This is now the fourth ever pandemic alert to be raised, since the first "Spanish" flu in 1918-1919 which killed 50 million people; the "Asian" flu in 1957; and the "Hong Kong" flu in 1968.

According to WHO's scale of pandemic alerts, the virus has moved to Phase 6 - the highest level - meaning the virus is being passed freely between people without easily traced chains of infection in two or more regions in the world.

So far, there have been 28,774 cases of the flu in 74 countries, with 144 deaths.

Although experts say the virus is less lethal than expected, it was declared a pandemic as there have been large outbreaks around the globe.

World Health Organization Calls Swine Flu Outbreak a Pandemic [WashingtonPost]