WASHINGTON (AP) — The descriptions are haunting.

Some victims felt fine in the morning and were dead by night. Faces turned blue as patients coughed up blood. Stacked bodies outnumbered coffins.

A century after one of history's most catastrophic disease outbreaks, scientists are rethinking how to guard against another super-flu like the 1918 influenza that killed tens of millions as it swept the globe.

There's no way to predict what strain of the shape-shifting flu virus could trigger another pandemic or, given modern medical tools, how bad it might be.

But researchers hope they're finally closing in on stronger flu shots, ways to boost much-needed protection against ordinary winter influenza and guard against future pandemics at the same time.

"We have to do better and by better, we mean a universal flu vaccine. A vaccine that is going to protect you against essentially all, or most, strains of flu," said Dr. Anthony Fauci of the National Institutes of Health.

Labs around the country are hunting for a super-shot that could eliminate the annual fall vaccination in favor of one every five years or 10 years, or maybe, eventually, a childhood immunization that could last for life.

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Fauci is designating a universal flu vaccine a top priority for NIH's National Institute of Allergy and Infectious Diseases. Last summer, he brought together more than 150 leading researchers to map a path. A few attempts are entering first-stage human safety testing.

Still, it's a tall order. Despite 100 years of science, the flu virus too often beats our best defenses because it constantly mutates.

Among the new strategies: Researchers are dissecting the cloak that disguises influenza as it sneaks past the immune system, and finding some rare targets that stay the same from strain to strain, year to year.