MMR is a live attenuated measles-mumps-rubella (MMR) vaccine used to prevent measles, mumps, and rubella. Two doses are usually required, and in some areas, three doses are given. The first dose is usually given at <12 months of age and the second dose at <24 months of age. The number of doses and the timing of vaccination may vary slightly depending on the CDC in each region, but the common timing of vaccination is: 1 dose of MMR at 8 months of age and 1 dose at 18-24 months of age. The first dose is used as a basic immunization shot, and some children may produce less antibodies after the first dose, or may not even produce the corresponding antibodies to play a better role in immunization, so it is usually necessary to give the second and third doses at 18 months and 6 weeks of age as a booster immunization shot to increase the amount of antibodies produced by the body. For children who have already missed the vaccination time, their families can also ask at the vaccination site for the specific time of the catch-up vaccination. In addition, children who are allergic to vaccine components, immunodeficient, or in a state of illness are not suitable for vaccination and should be vaccinated after a doctor has ruled out contraindications.