Measles, a deadly disease that once killed approximately 6,000 people each year in the United States, had been eliminated in the country in 2000 due to a vaccine. However, vaccinations are only effective if people take them. And in recent years, more and more people have decided against getting themselves or their kids vaccinated. Scientists say those decisions have led to outbreaks of the disease like the one that began in December 2014 at Disneyland in California. Through Jan. 21, 2015, there had already been 59 cases of the measles from that outbreak. As a result, doctors have renewed calls for everyone to be vaccinated.