During the process of vaccination, some vaccinees may feel strong adverse reactions to the second vaccination. If the adverse reactions only intensify compared to the first dose, but no serious discomfort occurs, it is considered that it may be related to the poor condition of the vaccinator, local irritation, and the injection technique of the medical staff. However, if the discomfort is unbearable after the second vaccination, it is necessary to seek medical diagnosis and treatment as soon as possible. I. Normal reactions 1. Poor state of the vaccinated person: If the vaccinated person has poor living habits such as lack of sleep, frequent late nights and irregular diet before the second vaccination, resulting in a relatively low immune function, the adverse reaction will be stronger under the stimulation of the vaccine; 2. The second injection of vaccine is a process of strengthening immunity, which is a re-stimulation of the body’s immune system, and the immune response may be stronger than the first injection, resulting in more obvious adverse reactions in the vaccinator; 3. If there are strong reactions such as severe swelling at the vaccination site, large skin rash, persistent fever, dizziness, headache, nausea and vomiting after the second injection, there may be an allergic reaction, which should not be handled by oneself to avoid aggravation of the adverse reactions.