There is no significant difference between vaccination of the left arm and the right arm. The reason for clinically injecting the left arm more often is that the right arm is not injected in order not to interfere with daily activities as the right hand is used more. If multiple vaccinations are required at a given stage, it is recommended to alternate between the left and right arm in order to keep the pain from concentrating in the same location. The vaccination site is usually chosen at the deltoid muscle of the upper arm because there is less fatty tissue and more muscle tissue at the arm, and the blood supply will be relatively rich to effectively absorb the vaccine components. The physiological structure and muscle distribution of the left arm and the right arm are the same, so there is basically no difference in the absorption rate of the vaccine. However, since the right arm is used more frequently in daily life, most people choose to get the vaccine in the left arm to avoid pain in the arm after vaccination, which may lead to restricted activities and affect daily life. In addition, it should be noted that vaccination at the arm should be done by wearing loose clothing as much as possible before vaccination to reduce the friction of clothing on the vaccination site. On the day after vaccination, the vaccination site should be kept free of water and scratched as much as possible to avoid infection at the vaccination site. If there are any adverse reactions such as breakage and pus flowing from the local skin of the vaccination site, it is necessary to disinfect it properly. In addition, within 1 week of vaccination, it is recommended to eat a light diet, quit smoking and alcohol, and avoid spicy and fried foods as much as possible to avoid triggering or aggravating adverse reactions.