Vaccination is one of the effective methods to prevent various diseases at this stage of society, and there are familiar vaccines such as hepatitis B vaccine, rabies vaccine, HPV vaccine, tetanus vaccine, etc., as well as the new crown inactivated vaccine, which is used to prevent the new crown virus. Different vaccine types, different vaccination times, and different suitable populations: 1. Different vaccine types: Vaccines requiring three doses are mostly recombinant subunit vaccines, which are produced without the participation of live viruses and have a higher safety profile. The two-dose inactivated vaccine is the most common and the first to be put into use. Its principle is to prepare the live virus after inactivation by purification technology, and its vaccine components are similar to the structure of the virus, and the immune response is strong. In contrast, the one-shot adenovirus vector vaccine, which was the first to be researched but the last to be approved for use, stimulates the body to generate an immune response by replacing the viral gene and produces a protective effect; 2. The vaccination time is different: the interval between the two shots of the vaccine that requires two shots is 3-8 weeks, the interval between the two adjacent shots of the vaccine that requires three shots is 4-8 weeks, and the third dose needs to be completed within 6 months after the first dose; 3. The number of doses of the vaccine is different from that of the vaccine for the first dose: the number of doses of the vaccine for the first dose is less, and it is suitable for people who are in good health and need emergency injections in a short period of time, but the physical quality of the vaccinator is higher. The two-dose vaccine and the three-dose vaccine can produce antibodies in the body of the vaccinated person, but the antibodies are weak and have a short duration of validity, so they cannot play an effective role in immune protection. The third vaccination is called a booster, i.e., a boosted immunization, which can make the antibodies produced more resistant and have a longer-lasting effect on disease prevention. These three types of vaccines are all permitted vaccines that meet our vaccine testing standards, so there is no rule as to which type of vaccine must be administered, and vaccinees can be administered according to their physical condition and wishes, combined with the recommendations of the vaccination officer.