Measles is a childhood infection caused by a virus. Once quite common, measles can now almost always be prevented with a vaccine.

Also called rubeola, measles can be serious and even fatal for small children. While death rates have been falling worldwide as more children receive the measles vaccine, the disease still kills more than 100,000 people a year, most under the age of 5.

As a result of high vaccination rates in general, measles hasn't been widespread in the United States for more than a decade. The United States averaged about 60 cases of measles a year from 2000 to 2010, but the average number of cases jumped to 205 a year in recent years. Most of these cases originate outside the country and occurred in people who were unvaccinated or who didn't know whether or not they had been vaccinated.