The inhaled vaccine, which takes the form of a fine powder, would be easier to administer in third world countries, as it does not require needles, syringes or water, and it does not need to been refrigerated during transport.

The vaccine, developed by researchers are Harvard University and tested by scientists at the University of North Carolina at Chapel Hill, is based on the Bacille Calmette-Guérin (BCG) vaccine commonly used throughout the world, which takes the form of weakened Mycobacterium bovis cells from the cow form of TB.

In the injectable form these cells are freeze dried, to preserve the cells in a weakened, but living during storage and transportation before use. However, vaccines prepared in this way need to be refrigerated throughout the transportation, and it must be mixed with water to be able to administer the vaccine through an injection, making it impractical to administer in the conditions of the developing world.

An inhaled dry-powder vaccine would solve some of these problems, as delivery through an inhaler is non-invasive and does not require water. "The vaccine is stable and can be transported and stored without refrigeration. In addition, the ease associated with simply inhaling the vaccine makes it suitable for delivery in any location without risk of contamination," says Tony Hickey from the University of North Carolina.

However, until now it had been hard to create a powder with fine enough particles to safely administer directly to the lungs. The team solved this by using special additives, and by using a spray drying process, where the cells are sprayed through heated gas to create a dry powder before storage.

"The uniqueness of this work is that it allows us to generate bacteria almost as individual cells, when actually they are not easy to separate," said Hickey.

It's possible that the inhaled vaccine may prove more successful than the injected vaccine, route of the vaccination is much closer to the route of infection, which would also be transmitted directly to the lungs.

"The immune system responds to disease with a cascade of defences that begin at the origin of infection. In TB the lungs are the initial site of infection. By co-opting the route of infection as the route of immunisation precisely the same cascade is evoked that will subsequently prevent infection," said Hickey.

When tested on animals the results seem very promising, with better results for the inhaled vaccine compared to the injected vaccine. "After delivering the vaccine to the animals and then exposing them to infectious micro-organisms only 1 per cent survive in the lungs of animals immunised by the pulmonary route while 5 per cent survive in those treated with the usual injection," said Hickey. However, he remains cautious as to how these results will translate to humans.