Image caption Lungs of a patient with a tuberculosis infection

A protein which could be targeted for a tuberculosis vaccine has been discovered by scientists at Imperial College London.

TB is caused by bacteria and the only vaccine against it, the BCG jab, is not very effective.

The disease of the lungs kills approximately two million people worldwide each year.

The charity, TB Alert, said the research was promising, but a vaccine was a long way off.

A better option

Scientists are aware that the BCG vaccine is not good enough.

Professor Ajit Lalvani, who led the research at Imperial College London, said: "Despite most of the world's population having had a BCG vaccination, there are still nine million new cases of TB every year, so we urgently need to develop a more effective vaccine for TB."

Researchers are trying to find new proteins which can be used in a vaccine to trigger an immune response and provide long-term protection against Mycobacterium tuberculosis.

Tuberculosis Tuberculosis is an infectious disease, which usually affects the lungs

It is transmitted via droplets from the lungs of people with the active form of the disease

In healthy people, infection often causes no symptoms

Symptoms of active TB include coughing, chest pains, weakness, weight loss, fever and night sweats

Tuberculosis is treatable with a course of antibiotics

In the UK, around 9,000 cases of TB are reported each year, mainly in big cities like London

Source: World Health Organization/HPA

The study, to be published in Proceedings of the National Academy of Sciences, identifies a new protein called EspC.

Professor Lalvani said: "We've shown that EspC, which is secreted by the bacterium, provokes a very strong immune response, and is also highly specific to Mycobacterium tuberculosis. This makes it an extremely promising candidate for a new TB vaccine that could stimulate broader and stronger immunity than BCG."

Consultant chest physician Dr Peter Davies, who is the secretary of TB Alert, said it was "promising" research.

He told the BBC: "We know of two other targets and the researchers have found a third, which could be useful.

"The trouble is it will take 10 years to find out if it will result in vaccine and whether that vaccine is any better than BCG."