The main purpose of vaccination is to help establish an immune barrier against viruses, but some adverse reactions can still occur after vaccination, mainly allergic reactions, localized skin reactions, systemic non-specific reactions and reactions to specific vaccinations. 1. Allergic reaction: Although most of the vaccines are safe, there are some sensitizing components due to the production process and substances, and allergic reactions can occur after vaccination. In mild cases, it is manifested as erythema, itching and rash at the vaccination site, while in serious cases, it can be manifested as acute allergic reaction of the whole body, such as respiratory difficulty caused by bronchospasm, multiple rashes and shock with decreased blood pressure. 2. Local skin reaction: the vaccine is mainly inoculated in the muscle parts, such as deltoid muscle or thigh muscle, which can cause redness, swelling, heat and pain at the injection site, which is a relatively common adverse reaction, when local skin reaction occurs, it can be treated with anti-infective drugs under the guidance of the doctor. 3. Systemic non-specific reaction: after vaccination, systemic non-specific reactions such as fever, drowsiness, poor mental health, anorexia, etc. can occur, generally only need to maintain a light diet and enough rest. 4. Reactions after specific vaccination: such as abdominal symptoms and diarrhea after rotavirus vaccine or polio vaccine, and dizziness and headache after influenza vaccine.