The MMR vaccine is valid for 11 years or the immunization period, so it is repeated once at the age of 11-12 years. The MMR vaccine protects against three infectious diseases, measles, mumps and rubella, and is a three-in-one vaccine. The MMR vaccine is a live attenuated vaccine and is usually administered to susceptible children over eight months of age by subcutaneous injection into the deltoid muscle. The MMR vaccine has an immunization period of 11 years, so children are re-vaccinated again at the age of 11-12 years in order to boost their antibodies. Measles, mumps, and rubella, all three are acute infectious diseases transmitted by the respiratory tract, occurring mostly in children and adolescents. The prognosis is generally good, but a few children may develop complications such as pneumonia and meningitis, and mumps can cause complications such as orchitis and ovaritis. The MMR vaccine can prevent the spread of three infectious diseases at the same time.