Tuberculosis is an infectious disease, which generally affects the lungs but can also affect other parts of the body. The disease is usually caused by the bacterium Mycobacterium tuberculosis (MTB). It is spread as an aerosol by people with active TB when they cough, spit, speak or sneeze. The classic symptoms of TB are chronic cough with blood-containing sputum, night sweats, fever and weight loss. Most infections are only latent and do not have symptoms. About 10 % of the latent infections progress to active disease which, if left untreated, kills about half of those infected.

Today an estimate of one-third of the world´s population is infected with TB. In 2016 there were more than ten million cases of active TB, which resulted in 1.3 million deaths – more than 95% occurred in developing countries.

Treatment requires the use of multiple antibiotics over a long period of time – typically up to four months. Antibiotic resistance is however a growing problem caused by the increasing rates of multiple drug-resistant tuberculosis strains (MD-TB).

A vaccine against TB – the Bacillus Calmette-Guérin (BCG) – was developed in 1921, and since then approximately four billion doses has been given as TB prevention worldwide. In Denmark BCG was taken out of the national child vaccine program in the 1980s due to the very low risk of getting infected (under 1 %). Danish scientists have found indications that the Calmette vaccine, apart from preventing TB, also has a positive effect on the immune system in general.