If you are in your 20s and are eligible for vaccination, you can catch up with BCG vaccination. BCG vaccine is a national class I vaccine, free of charge, in the newborn’s weight up to the standard birth that is inoculated with BCG, if the weight is not up to the standard, usually about 1 month BCG vaccine, can be effective in preventing tuberculosis infection. For 20-year-olds who have not been immunized with BCG, catch-up vaccination is also available. It is generally recommended that 20-year-olds need to have a PPD test before BCG vaccination. If the test is positive, they cannot be vaccinated with BCG vaccine because it cannot stimulate the body to produce effective antibodies even after vaccination. If the PPD test is negative, you can go for BCG vaccination in time. After BCG vaccination, local hypersensitivity reaction will be formed, and localized skin suppuration may occur. It is necessary to pay attention to observation to avoid infection, and to consult the doctor in time if there is any serious adverse reaction.