Bacillus Calmette-Gu erin (BCG) has been given to more than three billion persons since its first use in 1921. The routine is to administer a single dose of the vaccine at, or soon after, birth in countries where tuberculosis (TB) is endemic. Most industrialized countries administer BCG to selected high-risk groups only.BCG constitutes a group of strains of live, attenuated Mycobacterium bovis. The parental strain was created in 1908 after serial subculture of the virulent bacterium over a period of 13 years. The different vaccines in clinical use today emerged after subculture of this parental strain in many laboratories; these strains have varying phenotypic and genotypic characteristics [1].After its initial use as an oral vaccine, the intradermal administration of BCG is used most commonly today, as recommended by the World Health Organization (WHO) [2]. The vaccine affords approximately 80% protection against disseminated forms of TB in infancythat is, miliary TB and TB meningitis [3][4][5]. It is estimated that, each year, BCG prevents approximately 30 000 cases of TB meningitis and about 11 000 cases of miliary TB worldwide [3,6].The effectiveness of BCG in preventing pulmonary TB in adults and in infants is highly variable, with efficacies ranging between 0% and 80% (average 50%) having been reported from multiple clinical trials performed during the twentieth century [6]. The reasons for such variable protection may include geographic location, BCG strain variation, patient age at vaccination, the dose of vaccine, interference by environmental mycobacterial and helminthic infections, patient nutritional status, and host genetic factors [1,[6][7][8]. A recent Phase IV trial of BCG vaccination has addressed whether the route of vaccination may impact on BCG efficacy [9]. For this, the Tokyo strain 172 was administered at birth via either the intradermal or percutaneous route, in a randomized study, to 11 680 infants. Subsequently, equivalence in TB disease incidence over the first two years of life was demonstrated between the two groups. It follows that, although BCG has been used for more than AIDS and Tuberculosis: A Deadly Liaison. Edited
