The number of days of fever after MMR vaccination varies from individual to individual, and usually resolves on its own in 2~3 days. MMR vaccine is the abbreviation of combined live attenuated MMR vaccine, which is mainly composed of measles attenuated strain, mumps virus strain and rubella attenuated strain, and the main purpose of MMR vaccination is to prevent the occurrence of measles, mumps and rubella diseases. According to the relevant product inserts, a transient febrile reaction may occur within 1 to 2 weeks after vaccination. Mild febrile reaction can be relieved on its own after 2~3 days, no treatment is needed, if necessary, take proper rest, drink plenty of boiled water and pay attention to keep warm. Moderate fever reaction or fever persists without relief, physical methods or drugs (such as ibuprofen, etc.) can be used to treat the symptoms. In addition to fever, pain and tenderness may occur at the injection site. In most cases, it resolves spontaneously within 2 to 3 days. Scattered skin rashes may appear, usually for less than 2 days, and usually do not require special treatment. Fever after MMR injection is usually not a cause for alarm, but if the fever persists, it is recommended to consult a doctor promptly.