Vaccines are biological agents containing non-pathogenic antigenic substances that alter the pathogens and their toxicity products to make them non-toxic antigenic substances for humans, but for humans, vaccines, like bacteria and viruses, are exogenous pyrogenic sources that induce host cells to produce mediators that cause fever and raise body temperature. However, vaccines are different from bacteria and viruses in that they are not pathogenic and have no invasive power. Therefore, fever caused by vaccination is usually a transient low fever and does not require special treatment. Most fevers after vaccination occur within a few hours to 24 hours after vaccination and usually last 1-2 days, rarely more than 3 days, mostly low or moderate fever, but rarely high fever. Some live attenuated vaccines may show similar manifestations of mild disease, such as influenza vaccination, which may show transient flu-like manifestations and fever, usually within 24 hours after vaccination; measles vaccination may also show fever and transient rash. Generally, low fever does not require special treatment, and it is sufficient to ask the patient to drink more water to assist in physical cooling, while those with high fever may take antipyretics as needed. Vaccination usually results in fever within a few hours to 24 hours of vaccination, and the degree of fever varies from person to person, so it is recommended to deal with it according to the actual situation, generally not more than 3 days.