The benefit of BCG appears to be that it protects young children against disseminated and severe TB, e.g. TB meningitis and miliary TB.

It is important to note that a positive TB skin test in an adult is almost always considered the result of infection and should not be ascribed to residual false positivity effect from the BCG (particularly in countries where TB is endemic), unless the patient has had BCG vaccination as an adult. There is some data to suggest that vaccination with BCG after the first year of life can lead to persistent TST positivity in some cases, however this is not the case for those who were only vaccinated in infancy. Therefore, it is important to establish the timing of BCG vaccination in relation to the positive skin test. If there is any doubt, it is safest to assume that a positive skin test is due to infection not BCG vaccination.