The MMR vaccine generally enters its safety period after 14 days, but there is some individual variation and not complete consistency. The MMR vaccine is indicated for infants and children over the age of 8 months and can be used to prevent measles, mumps, and rubella. These three diseases are common infectious diseases in children, and vaccination is an effective preventive measure. After MMR vaccination, swollen lymph nodes, rash, and fever may appear in 7 to 12 days, which are usually mild and can be relieved on their own. Usually after 14 days, it can enter the safe period and the chance of adverse reactions is relatively low compared to before. However, there are some differences in personal constitution of different people, therefore, the time to enter the safe period will also have some differences. It is recommended to observe the physical condition of the child after vaccination, and consult a doctor promptly if there is any abnormality.