A UK laboratory is one of just three in the world working to develop a vaccine which would combat the spread of bird flu.
Researchers hope to have the basis for a vaccine in months
Researchers at the National Institute for Biological Standards and Control are using genetic technology to create the vaccine.
It would be essential if the virus began to spread between people.
However, so far, avian flu has only been passed from birds to humans through close contact.
Researchers are "building" a vaccine by combining avian and human flu genes. The genes from the bird flu virus are altered to make them safe.
Genetic material is then taken from a human flu virus. The resulting man-made combined virus should then provide the basis for a vaccine.
Researchers hope to reach this stage in around two months' time.
The live virus the scientists are working with was flown to the UK in a bomb-proof container from Vietnam. It has to be kept cold to keep it alive.
Scientists working in the laboratory have to take strict precautions to ensure that no one is exposed to the virus.
They wear protective suits and footwear, and the laboratory is a building within a building; all air and water which comes out is minutely filtered.
The air in the high-tech lab is sucked inwards when the door is opened to prevent air and bugs escaping.
Virologist Dianne Major told the BBC: "The virus we are using has killed chickens in South Asia, and it has killed humans.
"So we need to be careful and make sure that the people we are working with are protected from this virus, and also protect the environment."
Dr Alan Hay of the World Health Organization said it was hoping to stop the spread of the virus throughout South Asia.
He added: "Our main concern is that it will acquire the ability to spread widely throughout that particular region.
"Once it does that there will be little to stop it spreading to the rest of the world."