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Measles virus infection is one of the most important infectious diseases of humans and has caused millions of deaths since its emergence as a zoonosis thousands of years ago. Prior to the development and widespread use of measles vaccines, measles was estimated to cause between 5 and 8 million deaths worldwide each year. Remarkable progress in reducing measles incidence and mortality has been made, particularly in sub-Saharan Africa,1,2 as a consequence of increasing routine measles vaccine coverage and provision of a second opportunity for measles vaccination through mass measles vaccination campaigns (called supplementary immunization activities [SIAs]).3 In the Americas, intensive immunization and surveillance efforts have stopped endemic transmission of measles virus, in part based on the successful Pan American Health Organization strategy of nationwide measles vaccination campaigns and high routine measles vaccine coverage.4 In the United States, high coverage with two doses of measles vaccine has eliminated endemic measles virus transmission. These achievements attest to the enormous public health significance of measles vaccination.

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As measles control efforts are increasingly successful, public perceptions of the risk of measles diminish and are replaced by concerns of possible adverse events associated with measles vaccine. As a consequence, numerous measles outbreaks have occurred in communities opposed to vaccination on religious or philosophical grounds6 or because of unfounded fears of serious adverse events.7 An outbreak of measles in San Diego in 2008, imported from Switzerland, resulted in 11 additional cases in unvaccinated children and two generations of secondary cases.8 Among the 9 cases older than 1 year, 8 were unvaccinated because of personal exemption beliefs. In the first 4 months of 2008, more measles cases were reported in the United States than any year since 2001, and 63 of the 64 patients were unvaccinated or had unknown or undocumented vaccination status.9 Pediatricians can and should play a role in emphasizing the importance of childhood immunizations and dispelling myths and misunderstandings.

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Epidemiology

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Measles virus is one of the most highly contagious pathogens, and outbreaks can occur in populations in which less than 10% of persons are susceptible. Chains of transmission commonly occur among household contacts, school-age children, and health care workers. There are no latent or persistent measles virus infections that result in prolonged contagiousness and no animal reservoirs. Thus, measles virus can only be maintained in human populations by an unbroken chain of acute infections, requiring a continuous supply of susceptible individuals. Newborns become susceptible to measles when passively acquired maternal antibody is lost and are the main source of new susceptible individuals. Unvaccinated children contribute to the pool of susceptibles and to the spread of vaccine-preventable infectious diseases.10

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When endemic, measles typically has a typical temporal pattern characterized by yearly seasonal epidemics superimposed on longer epidemic cycles of 2 to 5 years or more. In temperate climates, annual measles outbreaks typically occur in the late winter and early ...

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