Measles in the United States since the Millennium: Perils and Progress in the Postelimination Era.

Airborne transmission and population susceptibility make measles one of the most contagious diseases plaguing humans. Prior to the licensure of the measles vaccine in 1963, measles caused millions of deaths around the world and hundreds of thousands of reported cases in the United States each year ( Fig. 1 ) ( 1 ). High two-dose vaccination coverage of school-aged children with the measles-mumps-rubella (MMR) vaccine achieved by enforcement of school entry vaccination requirements, systematic case-based surveillance, and rapid case investigations and outbreak responses, as well as better control of measles in the region of the Americas, resulted in the elimination of measles in the United States in 2000 ( 2 ). Elimination is the absence of endemic disease transmission (i.e., no epidemiological or virological evidence that measles virus transmission is continuously occurring for ≥12 months in a defined geographical area that has adequate surveillance). Fear associated with caring for a child with measles—whose terribly high fever and extensive rash could progress to pneumonia, encephalitis, or worse—was once universal but has now faded from communal memory. Pediatricians in the United States who began practice in the past 25 years may never have seen a patient with measles. America’s success in eliminating measles produced a paradoxical increase in our vulnerability. Attitudes and behaviors that became more prevalent since the beginning of the new millennium have resulted in decreased vaccination coverage in some communities to the point where an imported measles case could lead to very large or prolonged outbreaks. However, in 2015, the nation seemed to reach a tipping point. Public concern in response to a multistate outbreak originating in Disney amusement parks ( 3 , 4 ) pushed mainstream Americans into more vocal support for vaccination requirements and strengthened confidence in vaccines, which had seemed to be wavering ( 5 – 7 ).