It was a controversial move, but in 2005 scientists recreated the 1918 flu virus and looked at its effects on mice. Those in favor had argued that resurrecting the virus and studying it with modern molecular biology techniques could help fight future flu pandemics. Those against it thought it was too risky — terrorists could use the published sequence to make their own viral arsenal, they argued.
How they did it: A team of researchers extracted fragments of the virus from hospital samples and a flu victim who had been frozen in the Alaska permafrost since 1918. The RNA was changed into DNA, sequenced, and those sequences were fit together to get the full genome of the virus. Next they synthesized the virus DNA from the sequence, and injected it in human kidney cells to manufacture lots of the virus. When it was injected into mice, the virus was unexpectedly lethal — all died within six days.
What they learned: They then replaced some genes in the 1918 virus with others from modern, less deadly strains and identified the genes that gave the 1918 flu its virulent power and the ability to be passed between people.
The legacy: It wasn't the first virus recreated, but the research on the 1918 flu paved the way — philosophically as much as scientifically — for others to resurrect ancient viruses in the name of public health and medicine. And, a larger debate still continues about whether we should revive extinct species.