Humans are the only reservoir for measles virus; unvaccinated infants who have lost maternal antibodies account for the bulk of susceptible individuals. However, as measles vaccine coverage increases, the age distribution of the disease shifts upward: in the United States, adolescents and adults are the most likely age groups to acquire measles.

• Routine administration of the measles vaccine has markedly reduced worldwide mortality due to measles; in 2008, there were ~164,000 deaths.
• Pts are contagious for several days before and after the rash appears. The virus is spread primarily via respiratory droplets over short distances. Secondary attack rates among susceptible contacts are >90%.