In 1976, because of evidence of increased vaccine efficacy at older ages, the recommended age for vaccination was set to 15 months in 1976. Originally set at 9 months in 1963, it was changed to 12 months in 1965.

Although vaccination is currently recommended at 15 months of age for optimal efficacy, vaccin- ation as early as 12 months of age (on or after the first birthday) is considered appropriate evidence of measles immunity, and children vaccinated at 12-14 months of age are not routinely revaccinated. Vaccination as early as 6 months of age is recommended in settings of increased risk of disease.