Leg pain after the new crown vaccine and feeling tired all the time may be an adverse reaction to the vaccine, which is normal. It may also be caused by coupling reaction, which is abnormal. 1. Normal reaction: after the new crown vaccine, there may be slight dizziness, fatigue, arm pain and leg pain, always feel tired legs and other symptoms, these are normal, usually within two or three days the symptoms will gradually ease. 2. Coupling reaction: coupling reaction refers to the existence of some diseases before vaccination, and both appear at the same time during the incubation period or after vaccination. It is mainly related to the patient’s excessive fatigue, such as long-term chronic strain and strenuous exercise, resulting in leg muscle strain. After the body is injected with the vaccine, due to the body’s acclimatization process, the original leg muscle strain may be exacerbated and the symptom of leg pain after the new crown vaccine and feeling tired legs all the time may occur. If leg pain is not relieved for a long period of time after receiving the new crown vaccine, the patient should go to the hospital in time for relevant examinations and take effective treatment.