Measles cases on the rise – CNN's Elizabeth Cohen explains why

Global measles cases are spiking. There have been 220 cases of measles so far this year in the United States – more than triple the usual number. During the first half of 2011 in Europe, there have been over 26,000 reported cases of measles.

Ali Velshi and Christine Romans speak with CNN senior medical correspondent Elizabeth Cohen to discuss why reported measles cases are spreading and how you can avoid catching the disease.