It took a lot of digging to bring back to life the Spanish influenza virus of 1918. Some was done with invisible molecular primers in a PCR machine in Rockville. Some was done with pick and shovel in the frozen ground of Alaska. Either way, it was a huge amount of work on a project whose chance of success at the start seemed very, very slim. Now, it will go down as one of the most astonishing technical feats in the history of science -- the viral equivalent of bringing dinosaurs back in the fictional "Jurassic Park."

It may also prove to be unusually useful -- not an elaborate biological parlor trick, but a vital service to global public health.

The Spanish flu killed at least 50 million people around the world in slightly more than a year -- late winter 1918 into the spring of 1919. Researchers have never figured out what made the virus so lethal, in part because there were no samples to study. Although viruses had been discovered by 1918, the flu virus was not isolated until 1933.

With the genome of 13,600 nucleotides known and published in the journals Science and Nature, the 1918 virus is already shedding light on its own history. It was a bird virus that appears to have become a human virus through the slow accumulation of mutations, not through the sudden trading of genes with another flu strain.

It is also illuminating the possible future of viruses that are worrying flu experts now. Some of the H5N1 "bird flu" strains seen recently in 10 Asian countries carry a few of the mutations seen in the 1918 virus, suggesting that they, too, may be slowly adapting to human hosts.

With more work, scientists will probably be able to figure out why the 1918 strain was so dangerous. Experiments with the reborn virus began in August at the Centers for Disease Control and Prevention in Atlanta and have already answered some questions, which may lead to better vaccines and drugs.

The story of how this feat came about has several beginnings. In hindsight, it is clear that perhaps the crucial one occurred 55 years ago with Johan Hultin.