Measles is highly contagious, and it can lead to pneumonia, lifelong brain damage, deafness and even death. Fifty years ago, there were three to four million cases of measles every year in the United States, and four or five hundred deaths. Fifteen years ago, MMR — the Measles, Mumps and Rubella vaccine -- was thought to have eradicated measles in the US. But last year, there were 644 cases. And today, at least 70 people have measles in California and five other states, an outbreak that started at the "Happiest Place on Earth." Was it spread by visitors from other countries? Are too many Americans saying "no" to the MMR vaccine?