The World Health Organization has raised its pandemic swine flu alert level to phase 5 -- its second-highest level.
The move by the agency, which is the public health arm of the United Nations, is "a strong signal that a pandemic is imminent," according to published guidelines.
"The change to a higher phase of alert is a signal to governments [and industry] that certain actions now should be undertaken with increased urgency and at an accelerated pace," said Dr. Margaret Chan, WHO's director-general, at a press conference Wednesday.
"The biggest question is this -- how severe will the pandemic be, especially now at the start," Chan said. "It really is all of humanity that is under threat during a pandemic."
Practically speaking, the shift is crucial to mobilize pharmaceutical companies and governments to start manufacturing adequate antiviral drugs and expedite the creation of a vaccine against swine flu.
It also places the world a single step away from an official global pandemic.
President Barack Obama pledged "great vigilance" in confronting the swine flu outbreak Wednesday night as it spread coast to coast across the U.S.
Despite calls from many U.S. lawmakers for tightening controls over the Mexico-US border, Obama ruled out that option, even though the swine flu outbreak has been at its most virulent and may have begun there.
"We have been preparing all along as if this is going to be stage 6," Secretary of Homeland Security Janet Napolitano said at a press conference this afternoon before the WHO announcement. "Our efforts have been to stay ahead of whatever number WHO assigns."
Health and Human Services Secretary Kathleen Sebelius said at the same conference that the change in designation should not inspire undue worry.
"Panicking is probably not very helpful," she said. "What's helpful is turning this concern and worry into action steps."
In the United States, the swine flu virus has spread to 11 states and infected 94 people, according to the U.S. Centers for Disease Control and Prevention.
Appoximately 160,400 children across fourteen states will stay home from school on Thursday.
Five more states -- Arizona, Michigan, Mass., Nevada and Maine – each now have at least one confirmed case.
The latest state to report infections is Maine, with three new cases, according to Gov. John Baldacci, who says all those stricken are at home recovering .
In addition to the Maine, Richard Besser, acting director of the CDC, said there were now 51 cases in New York; 16 cases in Texas; 14 cases in California; two cases each in Massachusetts, Michigan and Kansas; and single cases in Arizona, Nevada, Indiana and Ohio.
The CDC has not officially added the Maine infections to their totals, which stand at 91 confirmed cases.
The announcements came on the same day that federal health officials reported the swine flu death of a 22-month-old baby boy in Texas -- the first known U.S. fatality from the outbreak.
The baby, who died at Texas Children's Hospital in Houston Monday, was from Mexico and was in the United States to visit family in nearby Brownsville, Texas, officials said. The death is the first linked to swine flu to occur outside of Mexico.
"This is obviously a serious situation," said President Obama of the developments today. He further urged local health departments to watch for new cases -- and for schools to "strongly consider" closing their doors if the virus is suspected or detected among students or staff.