Scientists at a Dutch university have created a deadly, highly contagious strain of avian flu in the laboratory – and now they want to publish exactly how they did it. The research was funded by the U.S. National Institutes of Health, which will decide soon how much of the research should be published.

The discovery has bred fears of bioterrorism.

“The fear is that if you create something this deadly and it goes into a global pandemic, the mortality and cost to the world could be massive,” a U.S. government official said on condition of anonymity. “The worst-case scenario here is worse than anything you can imagine.”

A team of scientists at the Erasmus Medical Centre in Rotterdam were successfully able to mutate the H5N1 strain of the virus into a form that can be easily transmitted in the air.

The research was led by virologist Dr. Ron Fouchier, who described his work at a conference in September as “really, really stupid” – but ultimately helpful for vaccine development.

Since it first appeared in 1996, the H5N1 virus has killed hundreds of millions of birds, but only about 600 people who came into contact with infected poultry. Still, it’s a highly lethal virus, killing 60 percent of those infected.