Some vaccines are given in one dose, so one dose is sufficient. If the vaccine is a two-dose vaccine, one dose of vaccine without a second dose may not provide protection. 1. If there is only one dose of the vaccine, in this case, one shot of the vaccine can play a protective role and there is no need to take a second shot. 2. If the vaccine is given in two or more doses, and the vaccine is given in one dose without a second dose, the effect of the vaccine will be affected, and the vaccine will not be able to play the corresponding protective role, and it may also lead to the vaccine failure of the first dose. Therefore, after the first vaccination, the second vaccination should be given within the stipulated period of time so as to enhance the antibody activity. It is recommended that you receive the vaccine on time and for the full course of the vaccine in order to achieve the best protective effect. If you do not complete the second vaccination within the prescribed time, you only need to make up the vaccination in time. You should also make sure that you receive the same brand of vaccine to avoid adverse reactions.