The cause of persistent low fever in children after vaccination is due to the reaction to vaccination. Vaccines are mostly developed from viruses, bacteria and other pathogenic bacteria, and after vaccination of children, the body will produce protective antibodies against the relevant pathogenic bacteria, which will prevent and reduce the reaction to the pathogenic bacteria, which is beneficial to the body. However, some vaccine reactions are strong, and some children’s immune function is not perfect, which may cause persistent low fever after vaccination. If the child is in good spirits and eating is not greatly affected, he or she can drink more warm water and observe for a while, and most of them will subside on their own. If the fever persists and the child’s mental state is poor, blood tests can be performed and cephalosporin treatment can be added if the white blood cells are significantly high.