BCG vaccine was invented in the 1920s and is the oldest of the vaccines in use. As we are a large country with tuberculosis, it is important to improve immunity and prevent the onset of the disease. Most adults have some immunity to TB, but infants and children are largely immune to it. In order for infants and children to gain immunity to TB as well, BCG vaccination is mandatory for every newborn child in China. BCG vaccination is often referred to as the “first shot at birth” and prevents the occurrence of childhood tuberculosis. This vaccination has been effective in reducing the morbidity and mortality of tuberculosis meningitis and disseminated tuberculosis. However, many people have a question: Is there an immunization period after BCG vaccination? Is BCG vaccination a lifelong immunization? On this question, it is necessary to understand the history of BCG vaccine development first. Two French scientists invented the BCG vaccine after they failed again to vaccinate sheep with the tuberculosis vaccine on their farm. After 13 years of long-term cultivation and 231 consecutive generations, the virulence of Mycobacterium tuberculosis bovis was finally eliminated while retaining their properties that stimulate immunity in humans. Immunity mechanism The main function of BCG vaccination is to stimulate immune cells such as macrophages and lymphocytes to develop a “memory” of the tuberculosis bacilli, and when a person is infected with the bacilli again, a corresponding immune response is rapidly generated to kill the bacilli. The unvaccinated body is very slow to respond, leading to the aggravation and spread of TB disease. Therefore, BCG vaccination cannot completely protect TB from the enemy, but can only try to minimize the big things and minimize the small things, not to let TB bacilli multiply excessively, mobilize the body’s immunity to control them as soon as possible, and surround TB bacilli with macrophages and lymphocytes to form nodules, and eventually inject calcium into them continuously to calcify and heal them. The effectiveness of BCG vaccination in newborns has been clinically observed for more than 20 years, and the protection rate was found to be 82% in children <15 years old; 67% in 15-24 years old; and 20% in 25-34 years old. We speculate that BCG vaccine may no longer be protective 10-20 years after vaccination. Therefore, the prevention of tuberculosis should also focus on the development of hygienic habits and not rely solely on the vaccine. BCG vaccine does not prevent the recurrence of latent TB nor does it provide lifelong immunity.