BCG vaccination is given within 24 hours of the baby’s birth, but premature babies, especially those with a birth weight of less than 2.5 kg, do not need to be vaccinated for the time being. Babies who have not received BCG vaccination can be vaccinated directly if they are less than 3 months old. If they are over 3 months old but less than 3 years old, such babies need to have a PPD test done in advance if they want to receive BCG vaccination, and babies with negative PPD can be vaccinated. If the baby is 4 years old or older, the BCG vaccine is no longer available. BCG vaccine is a very effective vaccination against tuberculosis in children, and it gives children a special resistance to tuberculosis. There are some special babies who cannot be vaccinated temporarily, such as babies with very small birth weight or sick babies, if they are very sick, have respiratory and circulatory failure, etc., they may not be able to receive BCG vaccination temporarily, and can only be vaccinated after their condition has stabilized and their weight growth is better in all aspects. Babies with immunodeficiency cannot be vaccinated with BCG, especially those with primary immunodeficiency, because their immunity is low and BCG vaccination may cause the spread of tuberculosis.