The MMR vaccine is usually required twice, but in some areas three times. The MMR vaccine is usually required for susceptible infants and children over 8 months of age who have rubella, mumps and measles. This vaccine is usually required two to three times. The first vaccination is usually given when the child is 8 months old for basic immunization, and the second, usually at about 18 months of age. By completing two rounds of vaccinations, the child is equipped to fight off rubella, mumps and measles. In some areas, children are revaccinated when they are 4 to 6 years old to boost immunity. Mumps, measles and rubella can be spread by airborne droplets, and children are generally susceptible to them. They are common infectious diseases, so vaccination is very necessary. However, a small number of children in 7 to 12 days after vaccination, rash, mild fever, lymph node swelling in the neck or cheeks and other symptoms, usually after a period of time can be relieved on their own, during the period is not contagious, parents do not need to worry too much. If there are obvious symptoms of discomfort after vaccination, you should seek medical treatment promptly.