CNBC: In the experiments, conducted in the United States and the Netherlands, scientists created a highly transmissible form of a deadly flu virus that does not normally spread from person to person. It was an ominous step, because easy transmission can lead the virus to spread all over the world. The work was done in ferrets, which are considered a good model for predicting what flu viruses will do in people.
The virus, A(H5N1), causes bird flu, which rarely infects people but has an extraordinarily high death rate when it does. Since the virus was first detected in 1997, about 600 people have contracted it, and more than half have died. Nearly all have caught it from birds, and most cases have been in Asia. Scientists have watched the virus, worrying that if it developed the ability to spread easily from person to person, it could create one of the deadliest pandemics ever.