Children three years of age are not eligible for the New Crown Vaccine booster. A booster shot is given to those who have completed the basic immunization program for the New Crown vaccine and are 18 years of age or older to increase the protection rate and effectiveness of the New Crown vaccine. The vaccination itself involves injecting attenuated or inactivated pathogens directly into the body to stimulate the immune system to produce antibodies. A booster shot can effectively ensure the concentration of antibodies in the body and prolong the duration of antibody protection. Due to the imperfect development of the immune system of 3-year-old children, the safety of booster vaccination for children aged 3 years and below is not clear, so booster vaccination is not recommended when there is initial resistance in the body to avoid adverse reactions. Children three years of age should consult a physician at the vaccination site for advice before receiving the New Crown vaccine.