Under normal circumstances, vaccination is not followed by sequelae, but there is a possibility of adverse reactions to vaccines, which are due to the body’s immune system reacting to the vaccine out of self-protective mechanisms. With vaccination, the body can induce unhelpful or even harmful immune responses or non-immune reactions in addition to beneficial anti-infective immune responses to foreign antigen stimuli. Vaccination with inactivated or attenuated vaccines can cause local or systemic adverse reactions due to the action of foreign proteins and immune adjuvants. The severity of the reactions varies with the physique of the vaccinees: 1. Local reactions: Slight redness or hard nodules appear in the injected area after vaccination, and a slight rash or itching may occur, which usually returns to normal within 1-3 days on its own and generally does not require treatment. Keep the area clean and dry, and pay attention to drinking more water and rest. If there is obvious local infection or sterile abscess, it is necessary to seek medical treatment promptly. 2. Systemic reaction: the body temperature is elevated, usually not higher than 38.0℃, and symptoms such as headache, dizziness, and weakness may appear, which can be relieved by themselves if the symptoms are mild. If the symptoms of generalized rash, angioneurotic edema, or high fever, muscle and joint pain persist without relief or even worsen, or anaphylaxis and other abnormal phenomena appear, you should go to the hospital promptly. Under the guidance of the doctor, symptomatic treatment, such as the application of anti-allergy drugs to relieve rash symptoms or treat anaphylaxis, should be carried out. Under normal circumstances, people who are in good health before vaccination usually do not have serious abnormal reactions. Patients who are weak or have chronic underlying diseases should consult the medical staff of the vaccination center before vaccination, be cautious and closely observe the condition after vaccination, and seek medical consultation when necessary.