Sequential vaccination means the administration of the same vaccine at intervals (alternately) with different technical routes. Sequential vaccination refers to the vaccination of the same type of vaccine at intervals (alternately) with different technical routes. Commonly, it is a vaccination strategy in which different types of vaccines of the same species are administered at certain intervals and in certain doses, in order to improve the preventive effect or further reduce the risk of serious adverse reactions. The use of sequential booster immunization has two main purposes. First, different vaccines can complement each other. The second is that individuals with different body types may have more side effects to a certain type of vaccine, and the use of different technical routes of vaccination can avoid adverse reactions. For viruses that are highly mutable and difficult to deal with, sequential immunization is often used for vaccination. As the new coronavirus is constantly mutating, in order to improve the effectiveness of the existing new coronavirus vaccine and reduce the risk of adverse reactions, the World Health Organization has made relevant recommendations, and our country, in the light of its national situation and the situation of prevention and control of domestic epidemics, has put forward the initiative of sequential immunization with the new coronavirus vaccine.