April 29, 2009— Swine flu has pushed the World Health Organization to raise its pandemic alert level to phase 5, which means that a pandemic is imminent.

It's the second time in a week that the World Health Organization (WHO) has raised its pandemic alert level, which ranges from phase 1 (low risk of a pandemic) to phase 6 (a full-blown pandemic is under way).

"The biggest question is, how severe will the pandemic be?" WHO Director-General Margaret Chan said today in a news conference in Geneva. "We do not have all the answers right now, but we will get them."

Chan said the swine flu situation is changing rapidly and the swine flu virus is still "poorly understood."

Chan called on all governments around the world to "immediately activate their pandemic preparedness plan," noting that each country is free to make its own pandemic plans -- and that many countries have been working on pandemic preparedness for years, thanks to concerns about bird flu ( avian flu). "The world is better prepared for an influenza pandemic than at any time in history."

Earlier today, CDC Acting Director Richard Besser, MD, said that the U.S. is at a "pre-pandemic" level and that it matters less what the situation is called than what's being done about it, and that the U.S. is taking "aggressive" action to limit swine flu's impact on human health.

WHO Pandemic Levels

Here is a quick look at the WHO's pandemic alert phases:

• Phase 1: A virus in animals has caused no known infections in humans.
• Phase 2: An animal flu virus has caused infection in humans.
• Phase 3: Sporadic cases or small clusters of disease occur in humans. Human-to-human transmission, if any, is insufficient to cause community-level outbreaks.
• Phase 4: The risk for a pandemic is greatly increased but not certain. The disease-causing virus is able to cause community-level outbreaks.
• Phase 5: Still not a pandemic, but spread of disease between humans is occurring in more than one country of one WHO region.
• Phase 6: This is the pandemic level. Community-level outbreaks are in at least one additional country in a different WHO region from phase 5. A global pandemic is under way.

Note that all of those phases are about how the virus is (or isn't) spreading -- they're not about the severity of the disease.

91 Cases in U.S.

At least 91 people in 10 U.S. states have swine flu, and there has been one death of a swine flu patient in the U.S., according to the CDC.

The patient who died was a 22-month-old boy from Mexico who died at a hospital in the Houston area. He had several underlying health problems, according to the Texas Department of State Health Services.

 Here is the CDC's latest tally of lab-confirmed swine flu cases:

    * New York: 51 cases
    * Texas: 16 cases
    * California: 14 cases
    * Kansas: 2 cases
    * Massachusetts: 2 cases
    * Michigan: 2 cases
    * Arizona: 1 case
    * Indiana: 1 case
    * Nevada: 1 case
    * Ohio: 1 case

But the situation is changing so quickly that "these numbers are almost out of date by the time I say them," Besser said today at a press conference.

Besser noted that health officials expect to see a "spectrum" of disease severity in the U.S. "Unfortunately, I anticipate that we will see more deaths."

Swine Flu Numbers Changing Constantly

The CDC and the World Health Organization (WHO) only report lab-confirmed cases -- not probable or suspected cases -- and they only do it once a day. So there may be a lag time before cases confirmed at the state or local level make it into the official tally.

The WHO today reported 114 lab-confirmed swine flu cases worldwide, but that figure is based on yesterday's CDC numbers and doesn't include three cases reported in Germany, one in Austria, and additional cases in New Zealand.

"It is clear that the virus is spreading; we don't see any evidence that it's slowing," Keiji Fukuda, MD, the WHO's assistant director-general for health security and environment, said at a news conference in Geneva earlier today.

Swine Flu Vaccine Work Under Way

Scientists are already working on creating a vaccine against the new swine flu virus.

"We're in full gear; the process is more speedy than [it's] ever been before, " Kathleen Sebelius, the new Secretary of the Department of Health and Human Services (HHS), said today at a joint news conference with the HHS, CDC, FDA, and the National Institutes of Health.

A swine flu vaccine may be created by early fall, but that doesn't mean it will be ready for distribution by then, health officials noted at the news conference.

Developing a vaccine means conducting clinical trials to see if the vaccine is safe, if it works, and what dose is needed, Anthony Fauci, MD, director of the National Institute of Allergy and Infectious Diseases, said at the news conference.

Fauci predicted that clinical trials of a vaccine against the new flu virus -- which he calls the H1N1 virus -- will "probably begin within a couple of months" and take several months.

'Serious Virus'

During today's joint news conference, a reporter asked why officials are so concerned about the new flu virus, given the fact that normal seasonal flu kills an average of 36,000 people in the U.S. during a typical flu season.

The reason is that it's a new, unpredictable virus that "has pandemic potential," Fauci replied. "It really is something different."

"This is a serious virus, this is a serious outbreak," Besser agreed.

"You don't know if it's going to fizzle out in a couple weeks or become more or less virulent or severe in the diseases it causes," Besser said. "If we could see into the future, that would be wonderful. But that's not the case. That's why we're being aggressive."