Scientists have developed a deadly strain of bird flu in a bid to create a vaccine, but experts worry that this deliberately grown infection could pose a serious health and terrorist threat.

Researchers from the Erasmus Medical in Rotterdam mutated the H5N1 avian influenza by transmitting it through the air – a first of this kind. Previously, the contagious H5N1 bird flu was thought to be passed on by human contact only.

However, these findings, published in the Science journal, may have to stay on paper, as health experts believe that if the investigation was to go any further, it could be used to develop a biological weapon in a bioterrorist act.

The U.S National Science Advisory Board for Biosecurity are reviewing the findings by Dutch researchers and will assess whether it should be blocked from further use.

"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. The worst-case scenario here is worse than anything you can imagine," a senior U.S Government advisor was cited as saying in the Daily Mail.

Other critics include Thomas Inglesby from the Center for Biosecurity at the University of Pittsburgh, who told the New Scientist, "The benefits of publishing this work do not outweigh the dangers of showing others how to replicate it."

However, the lead researcher from the study, Dr. Fouchier, defended his findings, telling the New Scientist, "We know which mutation to watch for in the case of an outbreak and we can then stop the outbreak before it is too late. Furthermore, the findings will help in the timely development of vaccinations and medication."

The H5N1 bird flu has claimed the death of millions of birds and around 300 people worldwide since 2003.