Tuberculosis (TB) is a very important public health problem. It is estimated that in 2014, 9.6 million people developed TB, and almost 2 million people died of this disease, where India, Indonesia, and China presented almost half of the cases occurring in the world. TB is caused by a bacteria called Mycobacterium tuberculosis that is spread from person to person through the air, when someone with the disease coughs, talks, or sneezes. It is estimated that one third of the people infected with this bacteria do not get sick but still have the bacteria hiding in their bodies, in what doctors call a "latent" (or dormant) state.
There is only one vaccine currently approved for TB in humans, and it is called Mycobacterium bovis Bacillus Calmette–Guérin (BCG). This vaccine has been given to more than 3 billion people since it was developed in 1921, with around 115 million doses per year given to newborns. The BCG vaccine is made from living bacteria that have been weakened in the lab so that they are unable to cause disease. This type of vaccine, using weak but still living bacteria, is called a live attenuated vaccine.

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