Many vaccines on the market today require 2-3 doses, such as the New Crown vaccine and HPV vaccine. Without the second dose of the vaccine, there is generally no harm, but it may not fully achieve the purpose of disease prevention. Vaccines go through both pre-theoretical and post-clinical trials during the research process, and there is literature and clinical support for how many doses a human can receive to achieve or come infinitely close to the desired purpose, so vaccinations should be administered according to vaccine specifications. For many vaccines that require 2-3 doses, such as the domestic 2-dose vaccine, the main component of both the first and second doses is the inactivated New Coronavirus, and generally the body will produce antibodies after the first dose, but the protective effect on the body is only weak and short-lived, and it is only through the second dose that the body’s immune system is stimulated again and more antibodies are produced, which will have a long-lasting protective effect on the body. The protective effect will only last for a long time. For the inactivated New Crown vaccine, the second dose is usually given 3 weeks after the first vaccination and no later than 8 weeks, and in principle it is recommended to receive the vaccine from the same manufacturer at the same vaccination site. After vaccination, some people will not experience any discomfort, while a small number of people will show symptoms such as dizziness, weakness and muscle aches, which are common side effects of the vaccine and can generally improve within a few days, and can be treated by consulting a doctor if necessary.