After public outcry against research into avian flu strains that can be transmitted among mammals, 40 of the top scientists working on the influenza strains signed a voluntary moratorium on research last January. The goal of the pause was to properly—and publically—weigh the potential risks and benefits of such investigations.

Critics of the research noted that the viruses under study—versions of the form known as H5N1—could be used as a bioweapon or might accidentally escape from a lab. Research supporters argued that without this research we could be caught unprepared if a pandemic were to emerge naturally and we did not know how to detect or fight it.

Now the same 40 signatories have pronounced that the work on H5N1 transmissibility should recommence in nations where it is permitted. The announcement was made public online January 23 jointly in the journals Science and Nature (Scientific American is part of Nature Publishing Group).

The U.S. has still not ruled on the fate of the research by labs in this country or by those receiving U.S. funding. But investigators in the Netherlands, Canada, China and elsewhere can now return to their studies of how H5N1 could mutate to create a human pandemic.

"We fully acknowledge that this research—as with any work on infectious agents—is not without risk," the signatories noted in their open letter. "However, because the risk exists in nature that an H5N1 virus capable of transmission in mammals may emerge, the benefits of this research outweigh the risks."

H5N1 is currently a threat for birds around the world. Should it become transmissible among humans, it has the potential to become a deadly global pandemic. Flu researcher Ron Fouchier, of the Erasmus Medical Center in the Netherlands, announced in September 2011 at an influenza meeting in Malta that he and his colleagues had created a strain of H5N1 that was transmissible among ferrets, the best animal model we have to study flu. By that winter, news of the development had spread, and concerned researchers, policy makers and public called for such research to end.

Fouchier and others have argued that this sort of research—when conducted under proper security conditions, such as in labs designated biosecurity level three-enhanced—is necessary to learn how to detect an emerging pandemic and to create the drugs and vaccines to diminish its ferocity. And the risk of details from the research being used for malicious purposes are quite small, he noted in a press conference about the decision to lift the voluntary research moratorium. Details of the ferret studies were published—after much debate—in June 2012.

The strain of H5N1 from the ferret studies needed only nine genetic mutations to transform from the standard avian flu into an infection that could be transmitted easily—say, via a sneeze—among ferrets. "Nine mutations for the influenza virus is almost none," Yoshihiro Kawaoka, of the University of Wisconsin-Madison, noted during the press conference. Two mutations have already been circulating in wild strains, "so that risk already exists in nature," he noted.

Knowing what mutations the virus needs to become transmissible among mammals should help improve surveillance, Fouchier noted during the press conference, fighting back a cough. "We can already use it to define the mutations that cause it to become airborne," he said. Further research could also improve drug development. "With these viruses in hand, we can better identify vaccines and drugs," he noted. Without being able to study H5N1 pandemic strains specifically, researchers are confined to using seasonal strains and avian influenza to test potential vaccines and antivirals. And different strains respond differently to various treatment and prevention measures. "You want to choose the right strain for better protection," Kawaoka added.

While many researchers across the globe prepare to resume research on H5N1 transmission, others, such as Kawaoka, wait with baited breath for the U.S. government to make a decision on whether and/or how it will allow—and fund—such research. "It's in their hands," Kawaoka said.