ROTTERDAM, THE NETHERLANDS — Locked up in the bowels of the medical faculty building here and accessible to only a handful of scientists lies a man-made flu virus that could change world history if it were ever set free.

The virus is an H5N1 avian influenza strain that has been genetically altered and is now easily transmissible between ferrets, the animals that most closely mimic the human response to flu. Scientists believe it’s likely that the pathogen, if it emerged in nature or were released, would trigger an influenza pandemic, quite possibly with many millions of deaths.

In a 17th floor office in the same building, virologist Ron Fouchier of Erasmus Medical Center calmly explains why his team created what he says is ‘probably one of the most dangerous viruses you can make’-and why he wants to publish a paper describing how they did it. Fouchier is also bracing for a media storm. After he talked to ScienceInsider yesterday, he had an appointment with an institutional press officer to chart a communication strategy.

Fouchier’s paper is one of two studies that have triggered an intense debate about the limits of scientific freedom and that could portend changes in the way U.S. researchers handle […]