On Apr. 2, 2008, the U.S. Centers for Disease Control and Prevention (CDC) issued Health Advisory in response to widespread measles outbreaks in U.S. During 2000–2007, a total of 29–116 measles cases were reported annually. However, during January 1–Apr. 25, 2008, a total of 64 confirmed measles cases were preliminarily reported to CDC, the most reported by this date for any year since 2001. Of the 64 cases, 54 were associated with importation of measles from other countries into the U.S., and 63 of the 64 patients were unvaccinated or had unknown or undocumented vaccination status.