A group of the leading virus experts in the U.S. has called for new, permanent restrictions on research in the face of a new genetically engineered flu virus that could kill half the population of the world.

Scientists are currently observing a 60-day moratorium on research into the bird flu virus, after two groups found a way to make it infectious through airborne transmission.

An outbreak of this virus could be worse than the 1918 Spanish flu that killed tens of millions of people, warned Michael Osterholm – who has led research into previous dangerous outbreaks – at a public meeting on censorship in science in New York on Thursday night.

"Frankly, I don't want a virus out there that, even if it was 20 times less lethal, would still be the worst influenza pandemic in history," he said.

Bird flu, or HN51, has so far infected 583 people, but it can
currently only be caught by close exposure to infected birds.
Photograph: Sushanta Das/AP

Professor Osterholm is a member of the U.S. National Science Advisory Board for Biosecurity, which in December asked the journals Science and Nature not to publish the full research on the virus.