Vaccines are biological products used for vaccination and are made with various types of pathogenic microorganisms. Vaccines are divided into two types: live and dead vaccines. Some vaccines require two doses in order to produce a better immunization effect and to ensure that the patient produces his or her own antibodies, which can effectively fight the virus and achieve the purpose of disease prevention. However, not all vaccines require two doses; there are also one-dose vaccines and three-dose vaccines, such as one dose of BCG vaccination and three doses of hepatitis B vaccination. Take the inactivated New Crown vaccine as an example, this vaccine usually requires two doses. Inactivated vaccine is a vaccine in which the virus is inactivated after culture, and then purified after verification. The body does not produce antibodies or a small amount of antibodies after the first dose, and the body will produce enough antibodies after the second dose at an interval of about 3 weeks, so this vaccine is usually given in two doses. The first dose stimulates the immune system to produce memory cells, and the second dose enhances the antiviral immune memory response. The advantages of inactivated vaccines are a mature process, fewer side effects, and stable quality for easy transportation, storage and use. Therefore, no matter how many doses of vaccines are administered, they will bring many benefits to the body and more people will be vaccinated to better build up the immune barrier and keep the body away from diseases.