New Flu Pandemic Could Kill 81 Million

"We know that even if we have much lower numbers of deaths worldwide than in 1918, the world will be severely stressed," said Dr. Keiji Fukuda, coordinator of the World Health Organization's Global Influenza Program. "Speculating about the possible numbers is an interesting exercise, but the really important thing is, what do we do about it?"

Since the pandemic threat rose, with circulation of the H5N1 bird flu virus on a large scale in late 2003, the global community has bolstered its pandemic preparedness plans. Medical systems today are far stronger than they were last century, and the availability of antivirals and antibiotics _ which did not exist in 1918 _ should help greatly. Still, many of these advances remain out of reach for poor countries.

Another question is the impact a flu pandemic would have on those infected with HIV. Seasonal influenza exacts a heavy toll on those with weakened immune systems. So, in the case of a new pandemic flu, Murray's estimate might be optimistic.

And while the Spanish flu often has been regarded as a worst-case scenario, there is no guarantee the next pandemic will not be even more deadly. Despite the tens of millions of deaths the 1918 flu caused, the death rate among those infected was approximately 2 percent. The fatality rate for the H5N1 virus is about 60 percent.

However, experts think that if H5N1 were to evolve into a strain easily transmissible between people, it would also become less deadly.

"It's not in a virus' interest to kill its hosts so readily, otherwise it can't reproduce," said Dr. Ian Gust, a flu expert at the University of Melbourne, Australia.

Still, there is no guarantee that H5N1 would become less deadly.

If it doesn't, "we would be in for a devastating impact," said Gust. "All bets would be off."