Ron Fouchier of Erasmus Medical Center in the Netherlands is pushing for openness. He is the lead researcher on one of the studies that showed how the H5N1 virus can be transmitted through airborne droplets between ferrets, a model for studying influenza in humans.

In December a U.S. advisory board asked two leading journals, Nature and Science, to withhold details of the research for fear it could be used by bioterrorists.

Bird flu is already one of the most deadly, though it can only be acquired through contact with infected birds. The potential for it to pass between people, through sneezes and coughs, sparks fears of a global pandemic worse than the 1918-19 Spanish flu outbreak that killed an estimated 20 million to 40 million people.

In an opinion piece published in Science on Thursday, Fouchier argued for the release the research to help public health officials better prepare for a scenario where the virus could mutate and become more deadly, spreading from person to person via coughs and sneezes.

He emphasized that other researchers are close to the same findings, some of them inadvertently, and should be warned in advance how the virus could become airborne.

"We have identified, from the published literature, laboratories working with H5N1 viruses that may only require one to three mutations before the viruses used may become transmissible" via airborne particles, the Erasmus team wrote.

They did not identify the other laboratories, though other experts say they include facilities in both government and academia.

"We want them to be careful," Fouchier said in an interview. "They did not know that they were one or two or three mutations away" from having an easily transmissible mutant virus.

The request by the U.S. National Science Advisory Board for Biosecurity has set off an intense debate about how to balance the free flow of scientific information against the threat of an "Armageddon" weapon if that research falls into the wrong hands.

In a statement to Reuters, Science said that its "editors are optimistic that details regarding an information transfer mechanism can be resolved in a matter of weeks."

DEADLY IN MORE THAN HALF OF CASES

First detected in 1997 in Hong Kong, H5N1 has devastated duck and chicken flocks in countries such as Cambodia, China, Egypt, India, Indonesia, and Iran, and has reached the Middle East and Europe through wild birds.

Lab analysis has confirmed that 577 people have been infected, but there may be many uncounted cases. Of those, 340 died, a fatality rate never before seen from a flu virus: the Spanish flu killed an estimated 0.5 percent of those it infected, while seasonal flu in the United States kills about 0.003 percent of those who catch it.

In Indonesia, H5N1 killed 82 percent of those infected, says virologist Daniel Perez of the University of Maryland.

That off-the-charts fatality rate has not translated into a higher overall death toll because H5N1 is so difficult to catch. But if it could be caught by inhaling or ingesting viral particles released from another infected person, then the high transmission rate combined with the high fatality rate could prove devastating.

Science on Thursday published two papers arguing for censorship of the studies and two arguing that release of the information could help public health agencies plan for a possible pandemic. In addition to the Erasmus study, scientists at the University of Wisconsin, Madison, have identified mutation that can make H5N1 transmissible from person to person.

Fouchier's team makes the case for openness so that responsible experts can see it before rogue elements do.

"Those in the know, know this," virologist Robert Webster of St. Jude Children's Research Hospital in Memphis, Tennessee, who advises the U.S. biosecurity board, told Reuters. "Multiple labs are very close."

So is nature. Individual mutations are already found in wild viruses, though none yet has all the mutations required for human-to-human transmission, Maryland's Perez said in an interview.

"But it is not hard to imagine that nature will eventually find a way to do that. It's not a question of if, but when," he said.

"LEGITIMATE NEED TO KNOW"

Webster believes that full, uncensored versions of the papers will be sent to ministries of health, national academies of sciences, and others that need to protect the public. Sources close to the debate say the journals are waiting for the U.S. government to work out a mechanism for conveying the uncensored information to those with a "legitimate need to know."

Knowing precisely which mutations allow H5N1 to be spread in air droplets would allow public health agencies to test for those mutations in viruses collected from birds and know if a pandemic might be imminent, argue the Erasmus scientists.

In particular, if surveillance programs detect the dangerous mutations in avian viruses in the wild, it should trigger more aggressive control programs. Similarly, developing a vaccine against a more-transmissible H5N1, as well as diagnostic tests and antiviral drugs, may require knowing those mutations.

The strongest voices against publishing details of the research include Michael Osterholm of the University of Minnesota and D.A. Henderson, who played a key role in the global eradication of smallpox.

They argue that the potentially dangerous information is unlikely to help public health authorities because in most of the countries where H5N1 is endemic, health and science agencies are incapable of conducting the surveillance and doing the genetic analysis to detect mutated strains in animals.

Osterholm and Henderson say the first priority should be "making every effort to ensure that this information does not easily fall into the hands of those who might use it for nefarious purposes."

Webster believes it is inevitable that the information will leak. But he sees value in restricting access, even if it is only in the short term.

"We can at least buy additional time by not putting it into the public domain right away," he said.

(Editing by Michele Gershberg and Xavier Briand)

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