Since there is a risk of vaccination failure if no scar is formed after BCG vaccination, a tuberculin test should be routinely performed 3 months after vaccination. If the tuberculin test is positive, even if there is no scar, it means that antibodies have been produced in the body. If the tuberculin test is negative, it means that the vaccination is invalid and the BCG vaccination should be repeated. Normally, hard nodules appear about 20 days after vaccination, which gradually soften, become pus, and crust over to form scars after breaking down. BCG vaccine is the most effective measure used to prevent tuberculosis and should be administered to healthy children within 24 hours of birth at full term.