The revision appears online Wednesday in the journal Nature.
It's the near-conclusion to a drama that pit efforts to learn how to thwart a global flu epidemic against concerns about helping terrorists create bioweapons. The second paper, which is more controversial because it involves what appears to be a more dangerous virus, is expected to be published later in the journal Science.
For some experts, the affair underscores a more basic question about whether creating potentially risky versions of bird flu is a good idea.
"Clearly, research like this can be beneficial" for dealing with the bird-flu threat, said Dr. Eric Toner of the University of Pittsburgh Medical Center's biosecurity centre.
But there's the question of calculating risk versus benefit, he said. "If we're taking a highly lethal virus and making it more transmissible, it's a tough judgment... These sorts of decisions should be made in advance of the research being done, not when the papers are ready for publication."
The bird flu that has spread among poultry in Asia for several years now can be deadly, but it rarely sickens people. And people generally catch it from chickens and ducks, not from other people. Scientists have worried that as virus strains mix in nature, they could produce a deadly bird flu that transmits easily from one person to another. That could set the stage for a flu pandemic.
The new studies come from two teams of scientists, one in a U.S. lab and another in the Netherlands. They created virus strains that spread easily among ferrets, which were used as a stand-in for people. The researchers wanted to study what genetic mutations helped the virus spread. That way scientists could identify such red flags in wild viruses and act quickly to avoid potential pandemic, as well as test vaccine and drugs.
The journals Nature and Science each planned to publish one of the studies.
But the federal government, which funded the research, asked the scientists not to publish details of their work. Officials were worried that the full papers would give bioterrorists a blueprint for creating weapons. That led to a wide-ranging debate among scientists, many of whom argued that sharing details of such work is essential in fighting the threat of dangerous viruses.
Both teams eventually submitted revised versions of their research to a U.S. biosecurity panel. That group and, later, federal health officials agreed to support publication. For one thing, the panel said, it would be difficult for others to do harm using the data provided, and for another, scientists had good reasons for publishing the results.
Yoshihiro Kawaoka of the University of Wisconsin-Madison, who led the research being reported Wednesday, said last month that the changes to his paper "were mainly a more in-depth explanation of the significance of the findings to public health and a description of the laboratory biosafety and biosecurity."
He and colleagues essentially created a hybrid of bird and human flu viruses, and identified mutations that let it spread through the air between ferrets. None of the infected animals died. The researchers also found evidence that existing vaccines would protect people against the hybrid.
The researchers said they didn't know whether the four mutations they identified would make a bird flu in nature more transmissible. But they said the results should help scientists find other such mutations and understand what makes bird flu spread in people.
The other paper reviewed by the committee, from a team headed by Ron Fouchier of Erasmus Medical Center in Rotterdam, the Netherlands, is going through peer review at the journal Science. The committee had more concerns about this paper, recommending publication of key parts by a split vote, versus its unanimous support of publishing all of the Kawaoka paper.
One difference is that while Kawaoka basically added a bird flu portion to an ordinary human flu virus, Fouchier's team made a bird flu virus more transmissible through mutating it. Kawaoka's approach appeared to produce less risk, Paul Keim, acting chair of the federal biosecurity advisory panel, told a Senate committee recently.
Toner said this week the hybrid Kawaoka's lab made would not be expected to be more dangerous than ordinary human flu, while the altered bird flu virus from the Dutch lab could be more lethal. So he said he's more concerned with the Dutch paper than Kawaoka's. But he said he would not second-guess the government's decision to support publishing the Dutch paper too.
Fouchier has said his altered virus, while easily spread between ferrets, did not kill them.
Richard Ebright, a molecular biologist at Rutgers University, said he's less concerned about publication of the papers than the fact that the federal government funded the research in the first place. "This is work that creates new biological threats," he said. "These viruses are dangerous and the ones that will come later (with further research) will be more dangerous."
Medical writer Lauran Neergaard in Washington contributed to this report.
Malcolm Ritter can be followed at http://www.twitter.com/malcolmritter
Journal Nature: http://www.nature.com