BUT THE VIRULENCE OF THE HYSTERIA IS OBVIOUS:

Flu's True Severity Is Still Unknown: Don't Leap to Conclusions, WHO Warns (Joel Achenbach and David Brown, 5/02/09, Washington Post)

The World Health Organization directly addressed the pandemic-versus-panic issue yesterday by cautioning the public against leaping to any conclusions about the virulence of the virus. It has yet to show lethality outside Mexico (the one person to die in the United States was a toddler who traveled from Mexico to Texas), though that doesn't mean it will remain a mild pathogen in the weeks and months to come, officials said.

Influenza is a simple virus, with just eight genes, but it makes poor copies of itself, leading to constant mutation. Most of those mutations are dead ends, but, given enough chances, the virus can become more infectious or more lethal. Although the United States is past its flu season, the Southern Hemisphere, where the virus has spread, is entering the cold months when influenza can become explosive.

Some positive news surfaced yesterday: Mexican scientists said the contagiousness of the swine flu is no greater than that of the seasonal flu that circulates every year. And a preliminary genetic analysis hasn't turned up any of the markers that scientists associate with the virulence of the 1918 "Spanish" influenza virus, said Nancy Cox, head of the flu lab of the Centers for Disease Control and Prevention.

The 1918-19 pandemic has cast a long shadow over today's health emergency. That virus circled the world, eventually infecting nearly everyone and killing at least 50 million people.

Jeffery Taubenberger, the National Institutes of Health researcher who reconstructed the 1918 influenza virus, said he is growing the new swine flu virus in his lab.

"We're very early on in figuring out what makes this virus tick. I am loath to make predictions about what an influenza virus that mutates so rapidly will do," he said. But he believes it will spread across the planet: "My prediction is that this strain will continue to spread, and it is very likely to become a pandemic virus, if it's not already a pandemic now. That does not mean that this has to be a very severe pandemic like 1918."

Michael T. Osterholm, an epidemiologist at the University of Minnesota, said the situation is analogous to forecasting a hurricane when meteorologists know only that there is a high-low pressure gradient in the Atlantic. "Everyone in one week wants an answer as to what it will do. Anyone who gives you an answer right now, do not listen to them about anything else because you cannot trust them," Osterholm said.

WHO spokesman Gregory Hartl noted yesterday that the public may misunderstand the word "pandemic." The term refers to where an illness spreads, not its severity.

A major unknown is the swine flu virus's "case-fatality rate" -- the small fraction of infected people who die. For the 1918 influenza, it was 2 to 2.5 percent for the United States as a whole, but in military camps and on troop ships, the rate was a brutal 7 to 10 percent, and in some Inuit villages, it soared to 70 percent.

The other two flu pandemics of the 20th century, however, were far milder. The Asian influenza of 1957-58 had a fatality rate of 0.2-0.5, and the rate during the Hong Kong influenza of 1968-69 was even lower, about 0.1 percent, close to what it is for seasonal flu.