Efficacy		In vaccine clinical trials, the amount of protection produced by an investigational vaccine against a specific infection or disease. A vaccine may be tested for efficacy in Phase III trials after (smaller) Phase I and Phase II trials demonstrate acceptable safety and promising immunogenicity.
ELISA (enzyme-linked immunosorbent assay)		A biochemical technique used mainly in immunology to detect the presence of an antibody or an antigen in a sample. It is often used to test whether a person is infected with HIV or has responded to a vaccine.
Epidemiology		The branch of medical science that deals with the study of incidence, distribution and control of diseases in populations.
Erythema		Redness of the skin. Erythema alone at the site of injection when a tuberculin (PPD) skin test is done does not indicate that a person has been infected with TB.
Extensively drug-resistant TB (XDR-TB)		TB that shows resistance to both first-line and second-line anti-TB drugs. In general, this means resistance to at least rifampicin and isoniazid from among the first line of anti-TB drugs (resistance to these is the definition of MDR-TB) in addition to resistance to any fluoroquinolone, and to at least one of three injectable second-line drugs used in TB treatment (capreomycin, kanamicin, and amikacin). XDR-TB emerges through mismanagement of treatment and can spread from one person to another.
Extrapulmonary TB		TB disease that occurs in places other than the lungs. The disease can show up, for example, in the lymph nodes, the pleura, the brain, the kidneys or the bones. Most types of extrapulmonary TB are not infectious.