UK researchers have made a crucial breakthrough in the development of a vaccine against the "Black Death".
Fleas transfer the plague from rats to humans
The bubonic plague, which killed millions in Europe in the Middle Ages, is now one of the most deadly agents available to terrorists.
Researchers at the Ministry of Defence's Porton Down laboratory say a vaccine could be licensed "within one to two years".
Around 2,500 cases of plague occur naturally each year across the world.
It is caused by the Yersinia pestis bacterium that can infect rodents. It is usually transferred to humans by fleas.
After someone has been infected, symptoms including fever, nausea, vomiting, diarrhoea and swollen lymph nodes which ooze blood, develop within two to eight days.
If it is untreated, bubonic plague kills around 60% of victims.
A vaccine could be used to protect troops against the dangers of biological warfare, and to protect people living in areas where the plague is rife
Porton Down researchers, led by Professor Rick Titball, recently carried out safety tests of the vaccine in humans.
They showed the vaccine produced no side-effects, meaning larger scale trials can go ahead.
A spokeswoman for Porton Down said: "This is a crucial stage, in that we have had one successful step to show the safety of the vaccine. Now we can move onto larger scale trials."
Professor Titball and his team identified two harmless proteins on the surface of plague bacteria which were capable of triggering an immune response against the disease.
He said work on a vaccine was even more significant now, as international terrorist organisations such as al-Qaeda could try to use non-conventional forms of attack, such as chemical or biological weapons.
Professor Titball warned a terrorist with a degree in microbiology would be capable of constructing a device using plague bacteria.
He said it was "one of the bio-terror agents about which we are most concerned."
Scientists at Porton Down have been working on a vaccine for bubonic plague since the 1991 Gulf War, when it emerged that Iraq had been developing stocks of chemical and biological weapons including plague, anthrax and botulinum toxin.
Troops fighting in the 2003 Gulf War were given a vaccine against anthrax.
Other scientists around the world are also working to develop a plague vaccine.
But Professor Titball said: "The Americans are very keen on our programme because we are well in advance of any other research projects developing a vaccine elsewhere in the world."