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WHO Ratchets Up Pandemic Alert Level a Notch

In another signal that the world may be closer to an influenza pandemic, the World Health Organization tonight announced that it has upped the pandemic alert level from 3 to 4, signaling increased human-to-human spread of a virus with pandemic potential. The decision was announced during a late-night press conference from Geneva by WHO's Assistant Director-General for Health Security and Environment ad interim, Keiji Fukuda. It was taken after a meeting of WHO's Emergency Committee, originally scheduled for Tuesday but held today in light of the rapidly escalating swine flu situation.

The pandemic alert level had been at 3 the past few years, to reflect the occasional human infections with the H5N1 avian influenza virus. At level 4, there are "small clusters with limited human-to-human transmission," according to WHO's Global Influenza Preparedness Plan, which also details a series of responsibilities and control options for both the agency and national governments. For instance, affected countries should give the outbreak top political priority and consider invoking emergency powers, the document says.

Although raising the threat level to 4 is a "significant step," Fukuda cautioned that "a pandemic is not considered inevitable at this time." As more is learned about the virus and the epidemiology of the disease, the threat level may rise to 5 or even 6, a full-blown pandemic, or it could drop back to 3, he said.

Some say that WHO appears to be dragging its feet in declaring a pandemic. "This virus seems to transmit pretty efficiently from human to human, and it's in several countries," says David Fedson, a retired pharma executive and flu vaccine expert. "What more do you need? This is a pandemic."

WHO does not recommend that countries close their borders or issue travel restrictions, Fukuda said, because the virus is already widely disseminated. The impact of travel bans on the spread of flu is controversial. Although a 2006 study suggested that the slump in air travel after 9/11 delayed that year's flu season by several weeks—and that the effect could be much greater if many more planes were grounded—several epidemiological models have suggested that unless a travel ban is "very, very draconian," it will have very little impact, says Fukuda. And the economic and social impact of such bans could be huge. "I completely agree with that," says epidemiologist and disease modeler Ira Longini of the University of Washington, Seattle.

Meanwhile, the number of reported cases from Mexico is rising rapidly. At a press conference today, Mexican Secretary of Health Jose Angel Cordova said the swine flu epidemic had likely killed 149 people, while nearly 2000 have been hospitalized with serious cases of pneumonia since it surfaced. Cordova also described what now appears to be the first confirmed case in Mexico, a 4-year-old boy who developed disease in late March/early April. The boy lives in Veracruz state, which has a large pig farm that has been the subject of much controversy, the Associated Press reports. No evidence exists, however, that pigs from the region spread the virus to humans.