evidence: So far this year, the country has seen more than 120 cases of measles, according to CDC data. That's more than double the number reported for all of last year. [...] CDC data showed that more than 80% of cases this year involved people who were either not vaccinated or whose vaccination status was unknown. About 13% of cases involved people who only received one dose of the measles vaccine. Public health officials recommend two doses. [...] Before a vaccine was introduced, the illness killed hundreds of people and sickened most children in the U.S. before they turned 15. That all changed in 1963 when a vaccine became available.