If the arm is swollen and itchy after the third vaccination, if there is no obvious rash or ulceration, most of them are caused by the vaccine not being completely absorbed or an allergic reaction has occurred. If the symptoms of allergic reactions are more serious, it is recommended to seek medical attention in time. If the same situation exists after the first two vaccinations, there is no need to worry excessively as it is mostly an adverse reaction after vaccination. When the vaccine stays in the local area and is not completely absorbed in time, local redness, swelling and pain will occur. Slight itching may occur due to the stimulation of the nerves in the surrounding tissues by the medicine or the body’s allergy to the vaccine, and itching may also occur after the vaccination when consuming or coming into contact with allergy-prone substances locally. Patients are advised to apply local heat to accelerate local blood circulation and promote the absorption of the vaccine, thus relieving the symptoms of redness and itchiness. If the rash is accompanied by other parts of the body, patients are advised to visit a hospital in a timely manner and take oral anti-allergy medications such as paracetamol, loratadine, etc. or use topical glyburide lotion under the guidance of a doctor. Note that patients should not use medication without permission to avoid affecting the effectiveness of the vaccine.