Atlanta ? It sounds like a sci-fi thriller. For the first time, scientists have made from scratch the Spanish flu virus that killed millions of people in 1918.

Why? To help them understand how to better fend off a future global epidemic from the bird flu spreading in Southeast Asia.

Researchers believe their work offers proof the 1918 flu originated in birds, and provides insights into how it attacked and multiplied in humans. On top of that, this marks the first time an infectious agent behind a historic pandemic has ever been reconstructed.

Like the 1918 virus, the current avian flu in Southeast Asia occurs naturally in birds. In 1918, the virus mutated, infected people and then spread among them. So far, the current Asian virus has infected and killed at least 65 people but has rarely spread person-to-person.

But viruses mutate rapidly and it could soon develop infectious properties like those seen in the earlier bug, said Dr. Jeffery Taubenberger of the U.S. Armed Forces Institute of Pathology.

“The effort to understand what happened in 1918 has taken on a new urgency,” said Taubenberger, who led the team that did the gene-sequencing for the project.

The research involved everything from excavation of human remains to application of the latest laboratory technology.

The Spanish flu of 1918 was a worldwide contagion that in a few months killed an estimated 20 million to 50 million worldwide, including roughly 550,000 in the United States.

In severe cases, victims’ lungs filled with fluid and they essentially drowned in a disease process that took less than a week. It was known for being particularly dangerous to young adults, a group usually less susceptible to flu complications than older people.

Scientists believe their reconstructed virus poses no public health threat because based on previous research, modern-day medicines are effective against the 1918 flu. And they think most people today are already at least partially immune.