Measles is the most transmissible infectious disease known in humans, and remains one of the top causes of death in children worldwide. Even in highly developed countries, measles kills approximately 3 of every 1,000 persons infected. While no treatment exists for measles, prevention in the form of vaccination has been available since the 1960’s. Despite the significant global morbidity and mortality of measles, considerable progress is evident. Just a decade ago, in 2000, measles killed an estimated 777,000 people a year worldwide. In 2010, measles killed only 160,000 worldwide – a testament to widespread use of vaccine.But concerns lurk, unnoticed for the most part. Despite the above gains measles is reemerging as a serious public health threat, and outbreaks are occurring even in highly developed countries where vaccine access, public health infrastructure, and health literacy are not significant issues. This is unexpected and a worrisome harbinger - measles outbreaks are occurring where they are least expected. As illustrated in the Table, since 2005 these outbreaks have also occurred in the U.S.—with surprising numbers of cases occurring in persons who previously received one or even two documented doses of measles-containing vaccine. In fact, as of September 2011, the U.S. has had 15 measles outbreaks with 211 confirmed cases—the highest number of cases since 1996 [1;2].