The absence of pus from the BCG vaccine does not necessarily mean that the vaccination has failed, only that the chances of failure are relatively high, and tests are needed to know whether the vaccination has failed.
If a child receives BCG vaccine without pus, there is a possibility of vaccination failure, but there is also a possibility of successful vaccination, in which case further PPD test (tuberculin test) is usually required.
The so-called PPD test is to inject the test solution into the skin of the flexor side of the forearm after routine sterilization and observe the result after 48 to 72 hours. If the child’s arm shows redness, accompanied by a hard nodule, it means the result is positive, and even if a scar does not form, it means that the vaccination has been successful.