What is the efficacy of BCG vaccine?
In a country like India where tuberculosis is endemic, children catch the germs early in life & develop primary TB. In children younger than 3-5 years of age, this can spread & lead to severe & serious forms of childhood tuberculosis. BCG being live vaccine itself induces a benign primary infection, which leads to some immunity. Such a child when comes in contact with a patient with tuberculosis can still catch the wild germ and develop primary TB, but the spread will be mostly prevented by previous BCG immunity. Hence such children will not develop serious forms of childhood tuberculosis. Such children when they grow as adults can catch tuberculosis again & develop adult form of tuberculosis which is a different type of tuberculosis altogether. Thus BCG does not prevent adult type of tuberculosis.
