IN JANUARY 2012 flu researchers around the world doffed their lab coats—at least in so far as their work concerned making deadly strains of bird flu deadlier still by enabling them to pass through the air between mammals. A year on, they have decided to end the self-imposed moratorium. In a letter published jointly on January 23rd in Nature, a British journal, and Science, an American one, the boffins behind the controversial studies explain that after much deliberation in assorted global fora they have concluded that the benefits of their efforts do, after all, outweigh the risks.

The voluntary break, originally intended to last 60 days, was called precisely because those risks looked substantial. For H5N1, to give the pathogen its proper name, is nasty. Of the 600 cases diagnosed in humans since 2003, almost 60% have been lethal. That made it three times deadlier than the "Spanish flu" of 1918, which claimed an estimated 100m lives. The reason bird flu has not beaten that awful record is that people can only catch the virus directly from a bird (usually a chicken). It has yet learn to jump from one person to another.

The furore that ultimately led to the moratorium erupted after it emerged that Nature and Science were about to publish research laying out how to teach H5N1 to fly between ferrets (which, as flu goes, are a good proxy for humans). That prompted an unprecedented move by America's government, in the shape of the country's National Scientific Advisory Board for Biosecurity, to request that the world's two leading scientific journals censor the papers, lest the knowledge fall into the wrong hands, or encourage similar efforts in labs ill-equipped to deal with dangerous infectious agents.

Ron Fouchier, of Erasmus Medical Centre in Rotterdam, and Yoshihiro Kawaoka, of the University of Wisconsin-Madison, who led the two controversial studies and co-authored this week's letter with 38 fellow researchers, always argued that these fears were exaggerated (as, indeed, has this newspaper). The sort of mutations they wrought could readily evolve in nature. Understanding them, they said, was vital to nipping a potential pandemic in the bud, by making it possible to monitor existing natural strains for the dangerous variants and helping to create effective vaccines.