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Predicting what direction flu will take is far from an exact science, experts say

ATLANTA - As cases of a unique form of swine flu erupt around the world, the inevitable question arises: Is this the big one?

ATLANTA - As cases of a unique form of swine flu erupt around the world, the inevitable question arises: Is this the big one?

Is this the next big global flu epidemic that public health experts have long anticipated and worried about? Is this the novel virus that will kill millions around the world, as pandemics did in 1918, 1957 and 1968?

The short answer is it's too soon to tell.

"What makes this so difficult is we may be somewhere between an important but yet still uneventful public-health occurrence here - with something that could literally die out over the next couple of weeks and never show up again - or this could be the opening act of a full-fledged influenza pandemic," said Michael Osterholm, an expert on global flu outbreaks with the University of Minnesota.

The new virus is called a swine flu, though it contains genetic segments from humans and birds viruses as well as from pigs from North America, Europe and Asia. Health officials had seen combinations of bird, pig and human virus before - but never such an intercontinental mix, including more than one pig virus.

More disturbing, this virus seems to spread among people fairly easily - a characteristic not generally seen in the swine flus that have occasionally jumped from pigs to people in recent years.

There's a historical cause for people to worry.

Flu pandemics have been occurring with some regularity since at least the 1500s, but the frame of reference for health officials is the catastrophe of 1918-19. That one killed an estimated 20 to 50 million people worldwide.

That pandemic began with a wave of mild illness that hit in the spring of 1918, followed by a far deadlier wave in the fall which was most lethal to young, healthy adults.

Pigs are considered particularly susceptible to both bird and human viruses and a likely place where the kind of genetic reassortment can take place that might lead to a new form of deadly, easily spread flu, scientists believe.

Such concern triggered public health alarm in 1976, when soldiers at Fort Dix, N.J., became sick with an unusual form of swine flu.

Federal officials vaccinated 40 million Americans. The pandemic never materialized, but thousands who got the shots filed injury claims, saying they suffered a paralyzing condition and other side effects from the vaccinations.

To this day, health officials don't know why the 1976 virus petered out.

Flu shots have been offered in the United States since the 1940s, but new types of flu viruses have remained a threat. Global outbreaks occurred again in 1957 and 1968, though the main victims were the elderly and chronically ill.

In the last several years, experts have been focused on a deadly form of bird flu that was first reported in Asia. So far, that virus has not gained the ability to spread easily from person to person. *