The World Health Organization is telling people to brace for the next flu pandemic.
In a late-night news conference Wednesday in Geneva, WHO Director-General Margaret Chan raised the pandemic alert level to its second-highest level, Phase 5. The WHO says that's a strong signal that a pandemic is imminent and that the time to get ready is short.
As Chan spoke, Mexican government officials imposed a virtual shutdown of the country's economy for five days, beginning Friday, to stem the spread of the newly discovered flu, which evolved from a swine virus. President Felipe Calderon said nonessential work will stop in government offices and businesses, and he urged citizens to stay home.
The official number of confirmed cases in Mexico was 99, with eight deaths.
In the United States, there were 114 confirmed cases of swine flu as of Thursday afternoon, including Georgia's first case. There has been one death, involving a toddler from Mexico City who died at a Houston hospital Monday night.
Other countries have reported 37 cases but no fatalities.
Immediate Action Needed
At the WHO, Chan told governments around the world that it's time to act.
"All countries should immediately activate their pandemic preparedness plans," she said.
That means, among other things, they should be on high alert for cases of flu and severe pneumonia. The WHO also will begin to mobilize its stockpile of anti-flu drugs, which contains 5 million doses. Chan has appealed to the World Bank for emergency funds to blunt the impact of the swine flu.
European Union health ministers have agreed to work "without delay" with drug companies to develop a pilot vaccine to fight swine flu. The ministers, who held emergency talks Thursday, also set up a special expert committee that will meet regularly to coordinate national measures, including travel advisories and communication campaigns to the public.
The threatened pandemic was the first item of business at President Obama's prime-time news conference Wednesday night. He struck a measured tone.
"The most important thing right now that health officials have indicated is that we treat this the same way we would treat other flu outbreaks, just understanding that because this is a new strain, we don't yet know how it will respond," the president said. "So we take some additional precautions — essentially take out additional insurance."
Obama put aside the possibility of trying to seal the nation's border with Mexico.
"It would be akin to closing the barn door after the horses are out," he said, "because we already have cases here in the United States."
But Obama did prepare Americans for a fair amount of disruption in the days and weeks ahead, as new cases of swine flu emerge.
"Our public health officials have recommended that schools with confirmed or suspected cases of this flu strongly consider temporarily closing," he said. "And if more schools are forced to close, we've recommended that both parents and businesses think about contingency plans if their children do have to stay home."
Scientists Warn Of Potential Changes In Virus
Confirmed and suspected cases of swine flu have shut down schools around the country — including the entire school district in Fort Worth, Texas. So far, at least 13 states have reported confirmed cases, and others are investigating illnesses that might be swine flu.
Chan said the biggest question now is how severe the pandemic will be.
Some scientists familiar with the evolving U.S. outbreak characterize swine flu in this country as a "moderately transmissable" virus similar in severity to ordinary seasonal flu. But Dr. Michael Osterholm of the Center for Infectious Disease Research in Minnesota warns that the virus may not remain relatively tame.
"You could very quickly see changes in this virus," Osterholm says. "Once the pig virus acquired the ability to transmit from person to person, all the other genetic roulette opportunities are there."
The greatest fear is that it will mutate into a far more dangerous virus. It also could acquire a gene that makes it resistant to anti-viral drugs, something that recently happened in a close cousin that causes ordinary flu.
Osterholm says the most important impact of the WHO's heightened alert involves "what we will do about a vaccine."
Bruce Gellin, deputy assistant secretary of health and human services, says the plan is to try to get the first doses of a tailored new swine flu vaccine onto delivery trucks in September. Over the following few months, the aim would be to get enough for all 304 million Americans.
Otherwise, U.S. health officials say the new WHO alert level does not materially change what they were already doing. "We're already trying to stay one step ahead of the virus," says Dr. Dan Jernigan, deputy director of the influenza division at the Centers for Disease Control and Prevention in Atlanta.
On Thursday, the CDC planned to ship out 500 hastily prepared test kits to state health departments, the first of many shipments. Each kit is enough to run 100,000 swine flu tests. That will speed up detection of cases, which will cause the number of reported cases to grow.
Even though the swine flu situation has evolved rapidly over the past two weeks, many public health officials were surprised by the WHO's decision to raise the alert level to the penultimate stage.
"It's really quite remarkable," says one California health official, who said she wasn't authorized to speak publicly. "I don't think in anyone's pandemic flu plan people were expecting to go from Phase 3 to Phase 5 within 48 hours." The WHO had raised the level to Phase 4 on Monday.
The WHO had been scheduled to hold a global conference call of its emergency advisory committee Thursday morning to discuss raising the level to Phase 5. But Chan canceled that meeting and instead made the decision on her own to heighten the alert level Wednesday night. She did not explain the factors that led to her decision.
During a media briefing just a few hours before Chan's announcement, her chief flu adviser, Dr. Keiji Fukuda, said the WHO would wait until it saw evidence that the swine flu virus was causing illness in the general community in at least two countries within a region, such as North America.
"What we are looking for," Fukuda told reporters, "is whether we're seeing transmission of the virus out in the community itself, in neighborhoods, among ordinary people who are just going around."
But apparently that's not what's happening so far in the United States.
Transmission In U.S. So Far Not From Casual Contact
Ira Longini of the University of Washington is collecting data on the U.S. outbreaks to plug into computer models that estimate the speed of transmission. "We're not seeing communitywide transmissions," Longini says. "Those would be contacts in casual settings such as subways or movie houses or restaurants or places where people come close to one another but don't spend a lot of time together."
Longini says all the U.S. cases of swine flu so far have involved someone who was infected in Mexico and then infected close contacts in schools or their own families — not casual contacts.
Fukuda says the world "is in the process of moving" to Phase 6 — a pandemic. However, he says, "we still need to see the evidence that we are there." Swine flu cases could develop explosively, fizzle out entirely or disappear with warm weather and come roaring back in the fall, as the fearsome flu pandemic of 1918-19 did, he said.
The WHO will be watching the Southern Hemisphere closely in the coming months, as it enters its main flu season.
NPR wire services contributed to this report.