Is Swine Flu Pandemic Imminent?

This is Part 3 of a 4-part LiveScience Special Report on the flu.

The swine flu drama is advancing like wildfire, with the Mexican death count rising steadily, U.S. cases doubling, and the World Health Organization moving a step closer late Monday to declaring the incident a full-on pandemic.

Will this flu become a global pandemic in humans, like AIDS or the "Spanish flu" of 1918–1919 which killed an estimated 50 million people in 18 months?

Declaring a pandemic is a big official deal. It's the more global version of an epidemic, which is a disease outbreak in a specific community or region or population. The word "pandemic" has a specific meaning to doctors and researchers, and once officials apply it to an outbreak, even more money and other resources are rushed to victims. Not to mention that there hasn't been a flu pandemic in more than 40 years (the "Hong Kong flu").

The World Health Organization elevated on Monday its global risk assessment for the new swine flu from Phase 3 to Phase 4. Phase 6 is a full pandemic — community outbreaks in two countries in two separate regions of the world (for now there is only a documented community outbreak in Mexico; the other cases worldwide are thought to be from people who visited Mexico). Phase 5 designates human-to-human spread of a virus into at least two countries in one region of the world. Phase 4 involves human-to-human transmission of an influenza virus able to cause "community-level outbreaks," such has definitely occurred in Mexico.

It is important to note: Phase 4 indicates a significant increase in risk of a pandemic but does not necessarily mean that a pandemic is a foregone conclusion.

Nonetheless, the U.S. government is taking aggressive action, as if a pandemic is imminent. Customs officials began checking travelers for illness upon entry to the nation's territories, according to the Associated Press. Millions of doses of anti-viral and other medications from a federal stockpile are being distributed.

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{{ video="LS_090428_pandemic" title="The Truth about Pandemics " caption="Dr. Marc Siegel explains why the term pandemic often inspires more fear than it should, how the media plays on fears, and how governments often make wrong and costly moves." }}

Determining a pandemic

Health agencies work together worldwide to define the word "pandemic" to avoid controversy over how to make this call, said Dr. George T. DiFerdinando Jr., a physician epidemiologist and professor at the University of Medicine and Dentistry of New Jersey-School of Public Health.

Individual countries each have their own ways of breaking it down, with the U.S. starting this weekend by declaring a public health emergency.

Once there is rapid human-to-human transmission, there is no question that a pandemic is occurring, DiFerdinando said. The Spanish flu was a good example of a rapid pandemic — it spread in a period of four to six weeks across every state in the nation.

For now, the swine flu is in a cluster in New York City, with and more and less individual cases in California, Texas and Kansas.

If it spreads throughout a community, or from one community to another, such as from New York City to New Jersey, things will start to ramp up terminologically.

The 1976 swine flu

A swine flu outbreak emerged in 1976 at Fort Dix in New Jersey. The national response to that event taught some hard lessons about efforts to head off a pandemic. The federal government initiated a vaccination campaign — some 40 million were inoculated. But a pandemic failed to materialize. Instead, some people got sick from something else — possibly the vaccine itself (and some of them died).

Leaders faced with disease outbreaks have to make decisions with a paucity of evidence, DiFerdinando said.

One benefit of the 1976 mishap was that the government learned how to vaccinate millions of people at once. Today, we all benefit from that with the annual availability of a new seasonal flu shot, a case made in "The Swine Flu Affair," a report by Richard Neustadt and Harvey Fineberg on the vaccination campaign and its repercussions, DiFerdinando said.

"This was a quick injection of federal money to push the pharmaceutical industry to produce vaccine very quickly, and that, in modern parlance, would be something like the American Reinvestment and Renewal Act (the 'stimulus bill') — government money to transform industry," DiFerdinando said. "It wasn't a conscious effort, but quickly people said, we have something new here."

Today, the pharmaceutical industry produces more than 130 million doses of seasonal flu vaccine annually. (Seasonal flu can kill people, but typically not at the global level or speed that a flu from a newly emergent strain does. With seasonal flu, some of us have some immunity to the flu. With newly emergent strains, none of us do, at least initially.)

"We are going to be closing in on having vaccine annually for anyone who desires it for seasonal influenza vaccine," DiFerdinando said. "That will save thousands of lives a year."

Another lesson from the 1976 incident was how to conduct a massive effort to track the spread of influenza and vaccine side effects among all Americans.

History of declaring pandemics

Back in the 1970s, the general medical thinking was that pandemics occurred every 10 years on average, since there had been a previous flu pandemic in 1968 and another in 1957. They were wrong. There hasn't been a flu pandemic since 1968. That 10-year thinking is part of what threw medical experts off in 1976.

"Predicting pandemics turns out to be imprecise in the medical and public health community," DiFerdinando said.

For instance, many medical professionals expected avian flu to become a human pandemic at some point in the past 10 years, but that has not occurred.

"If you can figure out what the frequency is [for flu epidemics] — you'd be quite famous," DiFerdinando said.

Flu shot, unlikely protection

People who got a flu shot this winter are probably unprotected from the new swine flu, DiFerdinando said.

"That would be unlikely to the point of saying, 'no,'" he said.

The vaccine is based annually on tiny virus parts that were selected six to eight months prior to flu season.

"The vaccine we got was a choice made last March or February about what was likely to be out there," DiFerdinando said. "This [new swine flu in humans] was not remotely on the radar screen, so the chance is virtually zero that what went into that vaccine would match what is in this new virus. We sure wish it would."

Still there is room for hope. There are some hints that the swine flu outbreak in the United States might be mild, DiFernando said.

"We'd like to hold on to that, but then reports out of Mexico is there are very severe cases," he said. "But if it turns out to be mild or contained, we are bound to learn something from this."

Part 4 of this series will be published tomorrow on LiveScience.

• Part 2: Q&A: Swine Flu Myths and Mysteries
• More Flu News & Information
• Flu Basics