BCG is the only widely used live bacterial vaccine. A live attenuated vaccines are produced by modifying a disease-producing virus or bacteria in a laboratory. The main aim of BCG vaccination is to induce a benign or artificial primary infection which will stimulate an acquired resistance to possible subsequent infection with virulent tubercle bacilli and thus reduces the morbidity and mortality from primary tuberculosis among those most at risk.

There are two types of BCG vaccine- the liquid(fresh) vaccine and the freeze-dried vaccine. Freeze-dried vaccine is more stable preparation than liquid vaccine with vastly superior keeping qualities.This vaccine is stable for several weeks at ambient temperature in a tropical climate and for up to 1 year if kept away from direct light and stored in a cool environment preferably refrigerated at a temperature below 10 degree.

The vaccine must be protected from exposure to light during storage and in field. Normal saline is recommended as a diluent for reconstituting the vaccine, as distilled water may cause irritation. The reconstituted vaccine may be used up within 3 hours. And left over vaccine should be discarded.This vaccine is taken as soon as a child is born and to those children who are said to be at the risk of early development of this disease.

Dosage:
for vaccination, the usual strength is 0.1 mg in 0.1 ml volume. The dose to newborn aged below 4 weeks is 0.05 ml. This is because the skin of newborn is rather thin and an intradermal injection with full dose in some of them might penetrate into deeper tissues.
The syringe and needle technique remains the most precise way of administering the desired dose.
The vaccine must not be contaminated with an antiseptic or detergent. If alcohol is used to swab the skin, it must be allowed to evaporate before the vaccine is given.
 
Age:
In countries where tuberculosis is prevalent and the risk of childhood infection is high, the national policy is to administer BCG very early in infancy either at birth or at 6 weeks of age simultaneously with other immunising agents such as DPT and polio.

Complications:
BCG has been associated with adverse reactions such as prolonged severe ulceration at the site of vaccination, disseminated BCG infection and death. Ulceration occur in less than one million vaccinations. The disseminated infection is usually associated with severe abnormalities of cellular immnity.

BCG vaccination is less effective in controlling tuberculosis as compared to active case-finding and chemotherapy, as BCG offers only partial protection. It can have only a relatively small epidemiological effect in that it will not contribute significantly to the reduction in the overall risk of infection in the community as a whole.
It can also be given at the same time as oral polio vaccine. It is a fundamental component of a national tuberculosis programme. Despite the contradictory evidence of controled trials, there is evidence that BCG plays a valuable role in preventing severe forms of childhood tuberculosis.

Today, BCG vaccination is a part of WHO Expanded Programme on Immunisation. The greatest need for BCG vaccination today is undoubtedly in the developing countries of the world where tuberculosis is still a major health problem.