MMR vaccine belongs to the National Immunization Program, most of the vaccinated people will not have fever, some of the vaccinated people usually have a low-grade fever within 24 hours after vaccination, and most of them will be relieved by themselves in 2~3 days. The MMR vaccine is composed of three viruses: measles, mumps and rubella, which are inactivated and injected intramuscularly. Because the germs injected intramuscularly into the body will cause the body to produce an anti-virus immune response, it will cause individual vaccinees to have a low or high fever within 24 hours. However, this is normal and will only last for 2 to 3 days without prolonged fever. If the vaccinee develops high fever or the fever lasts for a longer period of time, it should be considered that the vaccinee has a new infection during the vaccination process, before or after the vaccination, which is not related to the MMR vaccine, and the vaccinee should go to the hospital for a differential diagnosis in a timely manner, and then be treated symptomatically.