A live vaccine derived from a strain of Mycobacterium bovis, a form of bacteria that causes tuberculosis (TB). BCG vaccination is used to immunize against strains of tuberculosis that are resistant to the medications isoniazid and rifampin. Once BCG vaccine is administered, it reduces the ability of tuberculin skin tests to detect TB infection. Therefore, BCG vaccine is not recommended for an adult who is at high risk for contracting TB. Health care workers who have a negative PPD (purified protein derivative) result and are not immunodeficient may be considered for vaccination with BCG if they have a continued risk of exposure to TB. Children and infants may be candidates for BCG vaccination if they have close contact with people who have active, ineffectively treated, or drug-resistant TB and cannot take preventive treatment (isoniazid] or if they live in areas in which there are high rates of new TB infection that is unresponsive to treatment.