Bacille Calmette-Gueérin (BCG) vaccine		A live, attenuated strain of Mycobacterium bovis that has been used throughout the world since 1921. It is currently recommended by the WHO for newborns, for whom it is thought to reduce the risk of severe forms of childhood TB. While it provides some protection against severe forms of pediatric TB, it is unreliable against adult pulmonary TB. BCG can cause a positive reaction to the PPD tuberculin skin test, though this effect wanes over time.
Bacillus (pl. bacilli)		Rod-shaped (long and slender) bacteria, e.g., Mycobacterium tuberculosis.
Baseline tuberculin skin test		A tuberculin (PPD) skin test given to a person at the start of a tuberculosis contact investigation or tuberculosis surveillance program (e.g., employee surveillance at a health care facility).
B-cell (B-lymphocyte)		White blood cells of the immune system, derived from bone marrow and spleen. During infections, B-cells are transformed into plasma cells, which can produce large amounts of antibodies.
Blinded (or masked) study		A clinical trial in which participants and/or study investigators and staff do not know which treatment (experimental vaccine or control) each participant is receiving. (See double-blind study.)
Booster		A vaccine dose given after the primary dose(s) (see prime), to increase immune responses. A booster vaccine may be the same as the primary one, or different (heterologous prime-boost). (See prime-boost.)