Undisclosed quantities of the virus are being held in a high-security government laboratory in Atlanta, Georgia, after a nine-year effort to rebuild the agent that swept the globe in record time and claimed the lives of an estimated 50 million people.
The genetic sequence is also being made available to scientists online, a move which some fear adds a further risk of the virus being created in other labs.
The recreation was carried out in an attempt to understand what made the 1918 outbreak so devastating. Reporting in the journal Science, a team lead by Dr Jeffery Taubenberger at the Armed Forces Institute of Pathology in Maryland shows that the recreated virus is extremely effective. When injected into mice, it quickly took hold and they started to lose weight rapidly, shedding 13% of their original weight in just two days. Within six days, all mice injected with the virus had died.
In a comparison experiment, similar mice were injected with a contemporary strain of flu, and although the mice lost weight initially, they recovered. Tests revealed that the Spanish flu virus multiplied so rapidly that after four days, mice contained 39,000 times more flu virus than those injected with the more common strain of flu.
The government and military researchers who reconstructed the virus say their work has already provided invaluable insight into its unique genetic make-up and helps explain its lethality. But other researchers warned yesterday the that virus could escape from the laboratory. "This will raise clear questions among some as to whether they have really created a biological weapon," said Professor Ronald Atlas at the centre for deterrence of biowarfare and bioterrorism at the University of Louisville in Kentucky.
Publication of the work and the filing of the virus's genetic make-up to an online database followed an emergency meeting last week by the US National Science Advisory Board for Biosecurity, which concluded that the benefits of publishing the work outweighed the risks. Many scientists remained sceptical. "Once the genetic sequence is publicly available, there's a theoretical risk that any molecular biologist with sufficient knowledge could recreate this virus," said Dr John Wood, a virologist at the National Institute for Biological Standards and Control in Potters Bar.