The virus responsible for the 1918 Spanish flu pandemic, which killed an estimated 50m people worldwide, has been reconstructed by genetic engineering in a high-security US laboratory.

Preliminary studies show that it is an avian flu virus that mutated to spread quickly between people just as many experts fear will happen soon with the current H5N1 strain of bird flu in Asia. Details of the project are published today in the journals Science and Nature. The US National Institutes of Health approved the research, despite its apparent risk, because it will help scientists find new treatments for the most dangerous types of flu.