If the local redness at the injection site of BCG vaccine is 5-10 mm in diameter on average, it is a normal strong positive phenomenon, which means that BCG vaccination is successful, but if there is no local redness, or if the redness is <5 mm, it means that it is negative, which means that the vaccination is likely to be unsuccessful and the vaccine is not viable in the body, and you should go for a review of BCG vaccination and timely replanting. If no reaction has occurred by 3 months after vaccination, it is likely that the vaccination has failed and a tuberculin test should be performed at the vaccination site to decide whether to replant the vaccine. Confirmation of BCG vaccination results If you are worried that the vaccination has not been successful, you can do a tuberculin test (PPD skin test) to see if your child has been successfully vaccinated, and the PPD skin test requires 48-72 hours to observe the results. If the result is negative, the vaccination was unsuccessful and a follow-up BCG vaccination is required. If the result is positive, the vaccination is successful. If the result is strongly positive, further tests will be needed. It is important to confirm the negative skin test before the BCG can be replanted. Review of BCG The time to review the BCG vaccine is 3 months after the baby has received the BCG vaccine. No matter when your baby received the BCG vaccination, you should go to the designated health prevention agency after 3 months to check the effect of the BCG vaccination to make sure that the BCG vaccination has been given, which is called BCG review. Factors that make BCG vaccination unsuccessful Factors that make BCG vaccination unsuccessful include: insufficient dose of vaccination, uneven mixing of the vaccination solution, poor individuality of the baby, etc. The BCG vaccination is contraindicated for people who are suspected to have tuberculosis or are suspected to have been infected by tuberculosis bacteria. 2. Do not give BCG vaccination for acute fever, fever, skin diseases, severe eczema, chronic diseases, acute infectious diseases and premature babies or newborns weighing less than 2500 grams. 3. People with congenital or acquired immune deficiencies should never be vaccinated with BCG.