Appropriate age for measles vaccination in the United States.

The appropriate age for measles vaccination is determined by weighing the risk of measles disease and complications at a given age with vaccine efficacy at that age. In the United States, measles vaccine was initially used in children as young as 9 months of age because the disease was common and complications were greatest in persons less than 1 year of age. In 1965, when it became apparent that vaccine failure was unacceptably high in children less than 1 year and when epidemiologic analysis indicated that children greater than or equal to 1 year, particularly schoolchildren, were the primary focus of measles transmission, the vaccination age was raised to 12 months. In 1976, further studies showed efficacy was slightly higher at 15 months of age versus 12 months or 12-14 months of age. Because the risk of acquiring measles in children less than 15 months was low, the age for routine vaccination was increased to 15 months. This age recommendation may be appropriate for developed countries where the epidemiology of measles may be similar to the epidemiology in the United States. However, this age is inappropriate for many countries in the developing world where the risks of measles and complications from measles are high in young preschool children. In those countries, the recommended age for routine vaccination against measles is generally 9 months.