The Geneva-based World Health Organization today raised its alert level for the fast-spreading swine flu to its next-to-highest notch, signaling a global pandemic could be imminent.

The move came after the virus spread to at least 11 U.S. states from coast to coast and swept deeper into Europe.

"It really is all of humanity that is under threat during a pandemic," said WHO Director General Margaret Chan. "We do not have all the answers right now but we will get them."

Raising the alert level to 5, the second jump in three days, means a pandemic, or a global outbreak of a new virus, is imminent. It would be the first global pandemic in 41 years.

WHO and other health authorities have begun developing a vaccine against the disease, linked to 159 deaths in Mexico and one in the U.S. More than 100 swine-flu cases have been confirmed in North America, Europe and the Pacific, and the virus will probably spread, Keiji Fukuda, WHO assistant director-general for health security and environment, said today in a conference call with reporters.

"We have been preparing all along as if this is going to stage 6," Janet Napolitano, U.S. Homeland Security secretary, said at a news conference in Washington earlier today. "Our preparations are for a situation in which this does become a full-fledged pandemic."