The reaction period of AC group influenza vaccine is usually about two or three days. If the adverse reaction does not subside after more than three days, or tends to worsen, it is necessary to go to the hospital in time for medical consultation. It is normal for patients to have adverse reactions to AC group influenza vaccine, and not all vaccinated patients will have adverse reactions. Adverse reactions to vaccination may be related to the patient’s physical condition, the environment, the quality of the vaccine and other factors, and the normal reaction period is usually about two or three days, and the latest will not exceed three to five days. If a patient has a reaction after receiving the AC vaccine, it is considered to be caused by the reaction between the immune cells in the body and the drug, so parents are advised not to worry too much. After the vaccination, try to keep the vaccination slips, go home and let the child rest appropriately and pay attention to observe the state of the child, the adverse reaction, if more than three days, the adverse reaction is still not relieved, or there is a tendency to aggravate, need to go to the hospital in time to see a doctor. It is best to go to a regular, guaranteed vaccination site for vaccination, and before vaccination, you can ask the doctor for detailed advice on the precautions to be taken for vaccination and inform the doctor of your child’s specific situation.