If BCG vaccination is unsuccessful, there is no scar formation at the site of vaccination, and the tuberculin test is negative 3 months after vaccination, the above performance indicates that BCG vaccination is unsuccessful and a new vaccination is needed. The normal reaction after BCG vaccination is the appearance of small local hard nodules 2-3 weeks after vaccination, which gradually softens to form small pustules or abscesses and penetrates the skin to form shallow ulcers and scabs, which can leave permanent scars after the scabs fall off. BCG is a vaccine used to prevent tuberculosis and is administered within 24 hours after birth.