People who have received the third dose of the inactivated New Crown vaccine are significantly less likely to become infected than those who have not received it, but they can still become infected if they do not take the appropriate precautions. In China, it has been clinically proven that after two doses of inactivated New Coronary Vaccine (NCV), the human body becomes immune to the new coronary virus, but the duration and effectiveness of the immunity are not clear. The third dose of the inactivated novel coronavirus vaccine is a booster shot, which is usually given three or six months after the second dose. According to the latest research, after the third inactivated vaccination, the body’s immunity will increase rapidly, and even after infection, the proportion of patients with severe illness and mortality rate can be significantly reduced. However, the new coronavirus is constantly mutating, its transmission speed is fast, its transmission capacity is strong, the infected person’s viral load is relatively large, and the incubation period is relatively short, and all these characteristics have led to a reduction in the vaccine’s immune defense efficacy. Therefore, there is no guarantee of 100% avoidance of new coronavirus infection after three doses of vaccination. If the vaccinated person does not wear a good mask, does not pay attention to diligent hand washing, and comes into contact with an infected person, he or she may still be infected. Therefore, persons who have received three doses of the new coronavirus vaccine still need to take proper personal protective measures in order to reduce the risk of infection.