Some flu pandemics less deadly than others

[May 05, 2009]  NEW YORK (AP) -- In the next few days, the swine flu outbreak may become the world's first official influenza pandemic in 40 years. That won't be welcome news, but it's not as scary as it sounds.

After all, "pandemic" means only that a virus is circulating widely -- in this case, within the Americas and in another region, most likely Europe. It's about geography, not death tolls.

And it doesn't necessarily mean anything close to a replay of the event that makes public health planners shudder: the flu pandemic of 1918, which killed 20 million to 50 million people worldwide.

In fact, the world has had two flu pandemics since then, and their tolls were much lower. (And even those pandemics were far deadlier than this year's swine flu outbreak has been so far.)

"You have this wide spectrum," says Dr. Howard Markel, a medical historian at the University of Michigan. That shows "how predictably unpredictable these things are."

On Monday, the World Health Organization had its alert level set at Phase 5, which it calls a "a strong signal that a pandemic is imminent." Phase 6 would mean a pandemic has arrived.

U.N. Secretary-General Ban Ki-moon said on Monday that the WHO had no current plan to raise the alert level. And WHO chief Margaret Chan said, "We are not there yet."

There were little more than 1,200 cases of swine flu confirmed worldwide as of Monday, with fewer than 300 in the United States. In Mexico, where the latest count is fewer than 800 cases, officials lowered the alert level in the capital on Monday and said they will allow cafes, museums and libraries to reopen this week.

Dr. Richard Besser, acting chief of the federal Centers for Disease Control and Prevention, told reporters Monday the CDC expects the current outbreak to be declared a pandemic at some point. That won't change public health preparations in the United States, he added.

As of Monday, there were 27 confirmed deaths from swine flu, all but one in Mexico. But the flu is still moving into other countries, and scientists are watching it closely because the virus is a never-before-seen genetic mix that seems to spread easily.

Compared with the 20 million or more who died around the world in the 1918 disaster, the two other flu pandemics of this century have been milder. Worldwide, the Asian flu pandemic of 1957 killed only about 2 million.

The Hong Kong flu of 1968 killed about 1 million, but ordinary flu kills about 250,000 to 500,000 people each year. Within the United States, the 1968 flu pandemic killed about 34,000 -- roughly the same as the death toll from season flu every year.

Why the big variation in pandemic punch? It's a mystery.

Experts say the difference in death toll depends not only on how many people get infected but also on their medical vulnerabilities, as well as how lethal the virus is. Another factor is how effective prevention measures are.

Markel, whose research suggests non-pharmaceutical measures like school closings and banning public events reduced deaths in 1918, noted that health officials have been planning for a flu pandemic for several years. That's because of concerns over bird flu. Having such sophisticated detection and reporting systems in advance of an outbreak is "revolutionary," he said.

There are some hopeful signs about the swine flu virus:

• Lab studies show it appears to lack genetic traits that made previous flu viruses so deadly.

• Cases in the United States don't appear to be more severe than ordinary flu, although federal officials say they know little about the 35 people who were hospitalized.

• Markel said most people older than 55 have already faced a similar kind of flu virus, so their immune systems may already be primed to resist severe disease.

• The outbreak in Mexico, which began earlier than in the United States, appears to be waning.

Yet, Markel said, "we have to take these events very seriously" in wake of the 1918 disaster.

In 25 years as a physician, he noted, "I've never once had a patient say to me, 'Thanks for underpreparing.'"

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On the Net:

Pandemic history

Pandemic timeline

World Health Organization

[Associated Press; By MALCOLM RITTER]

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