In 2000, due to vaccination efforts, measles was declared eradicated from the U.S., but 2013 is projected to have the highest number of cases since 2000. Out of the 159 people in the U.S. who had measles this year, 117 had declined the MMR vaccine for philosophical/religious reasons.
A recent study by the CDC showed that approximately 90% of young children received the MMR vaccine in 2012, which is down from 92% in 2008. It is estimated that vaccine rates must be greater than 91% to control measles. Unfortunately, unvaccinated people tend to cluster together in social groups, making those groups at a much higher risk to themselves and others. This could lead to a large scale outbreak of measles in populations that are unvaccinated for health reasons or who have decreased vaccine protection.