(USA TODAY) -- Bird flu experts on Wednesday ended a voluntary halt on research into how to make the deadly H5N1 avian influenza capable of spreading to mammals, and perhaps rapidly to people.

The international moratorium began last year after an uproar over two studies that looked at genes that might make the bird flu readily transmissible between ferrets, a mammal stand-in for infection from person-to-person. Forty experts from nine nations now say they're ending the moratorium, citing safeguards in place against the release of their flu bugs.

The studies last year raised fears that the work could lead to the unintended release from labs of highly lethal bugs and that bioterrorists might use the studies as their cookbook.

In a letter announcing the end of the moratorium, published in the journals Science and Nature, the experts cited benefits to monitoring possible natural outbreaks of the disease and in testing possible vaccines. "We believe the public health benefits of H5N1 research outweigh the risks," says signer Yoshihiro Kawaoka of the University of Wisconsin. "There can never be zero risk in research, but we think the risk can be successfully managed."

Normally transmitted from poultry to people, the H5N1 virus has killed about 360 people since 2003, largely farmworkers in Asia and Egypt, according to the World Health Organization. Because the disease has a roughly 60% death rate, based on WHO case numbers, research has looked at how gene mutations might facilitate the spread of the disease from person to person.

In 2011, the two journals releasing the statement on Wednesday reported that a federal "biosafety" board had called for limiting information contained in two bird flu transmission studies, one headed by Kawaoka and another by Ron Fouchier of Ersamus MC in the Netherlands.

Originally set for only 60 days, the moratorium on the research was intended to allow research funders and public health authorities to create safeguards.

"We have done as much as we can as far as addressing the concerns," says Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases. He says a framework for evaluating the safety of proposed H5N1 research should allow the resumption of federal funding within weeks. "These decisions will always be made on a case-by-case basis, with public health a chief concern," Fauci says.

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