The MMR vaccine, which protects against measles, mumps, and rubella, is more than 97% effective when you receive the booster dose after the initial shot, which on its own is 93% effective. In the United States, measles cases have declined by more than 99% since the vaccination program started in 1963.﻿﻿ The MMRV vaccine, which also protects against varicella (chicken pox), is 95% effective.﻿﻿