Scientists have explained the decision to publish the full versions of two papers on the H5N1 bird flu virus just months after they had opted to release only edited versions.

At a Royal Society meeting, Paul Keim, acting chair of the US National Science Advisory Board for Biosecurity (NSABB), explained how the board had advised the US Government that two papers about the virus be published but in an edited form.

The two papers—one written by Ron Fouchier from Erasmus Medical Center in Rotterdam and the other by Yoshihiro Kawaoka from University of Wisconsin-Madison—detailed how they had mutated the H5N1 virus so that it could be transmitted among mammals by air rather than solely by close physical contact, explains Reuters.

The fear at the time was that these mutant strains could cause a pandemic if released by accident or on purpose by terrorists. NSABB instead opted to publish edited versions, allowing access to the full versions to only "select scientists,"says Discover magazine.

Reuters adds that the decision to censor the papers caused concern at the World Health Organization because it could "threaten the 'fragile' international collaboration that the WHO had assembled to combat avian flu." In particular, WHO was worried that countries such as Indonesia, which had taken years to persuade to hand over its samples of the flu virus, could stop cooperating.

However, on March 30, NSABB reversed its decision stating that "the data described in the revised manuscripts do not appear to provide information that would immediately enable misuse of the research in ways that would endanger public health or national security."

The papers will be published later this year, but Discover magazine reports that both authors have since revised their work. Fourchier told the audience at a Royal Society press conference that he has clarified, for example, that the airborne mutants of the virus did not kill the ferrets that were infected with it. "There was a misconception within NSABB about the lethality of our virus," says Fouchier.

However, it will be some time before the papers are published. Discover adds: "Both manuscripts still have to go through the usual process of peer review, and the US government hasn't weighed in yet. But should the process now go smoothly, nothing will be redacted from either paper. Fouchier has confirmed that his manuscript will include the full genetic sequence of his mutant strain."

Fouchier is also standing by statements he made when the existence of the mutant strains of the virus became public. He described the mutant H5N1 virus as "probably one of the most dangerous viruses that you can make." He told the Royal Society audience: "I'll stick by that comment without any problems. Maybe I'd put it slightly differently next time but it is the truth. Flu viruses are scary and if they acquire the ability to go airborne in humans, they cause pandemics."