Which manufacturer to give the third vaccine for the new crown needs to be judged specifically based on previous vaccinations. Currently there are two types of vaccines that can be used to implement booster immunization: 1. Inactivated vaccines: the production companies are Sinopharm Zhongsheng Beijing Company (i.e. Beijing Biological, including its original liquid distribution of Lanzhou Biological, Changchun Biological and Chengdu Biological), Beijing Kexing Company (also known as Beijing Kexing, Kexing Zhongwei, or Kexing Dalian), Sinopharm Zhongsheng Wuhan Company (also known as Wuhan Biological), and Shenzhen Container Vaccine. 2. Adenovirus vector vaccine: the production company is Tianjin Kangxinuo Company. At this stage, the strategy of “booster vaccination” is: homologous vaccination and sequential booster vaccination. 1. If the previous inactivated vaccine is the same as the first and second shots: in principle, use the original inactivated vaccine for booster; the first and second shots are different: in principle, give priority to the use of the same vaccine as the second shot for booster (in case there is no such vaccine, don’t panic, and use the same vaccine as the first shot for booster is also possible). 2. People who have completed 2 doses of vaccination with Shenzhen Kangtai vaccine will, in principle, continue to use the original inactivated vaccine for 1 dose of booster immunization. 3. If the previous vaccine was adenovirus carrier vaccine: it is sufficient to use the original vaccine for booster immunization, and the arrangement for subsequent additional booster immunization vaccines will be formulated separately according to the national deployment. 4. At present, there are two combination programs for sequential booster immunization: Inactivated vaccine (Vero cell) 2 doses of basic immunization + recombinant protein vaccine (CHO cell) 1 dose of booster immunization; Inactivated vaccine (Vero cell) 2-dose basic immunization + adenovirus vector vaccine 1-dose booster immunization.