A measles outbreak in the U.S. has grown to nearly 100 cases​​​. Here's what to know about measles vaccines and those who may need a booster.

As of Thursday, the CDC reported 93 cases of measles in the U.S. this year. 30% of the cases involved kids under five. 52% were ages 5 to 19. 16% were 20 or older. The vast majority were unvaccinated or had an unknown vaccination status. Only 4% reported getting one dose of the vaccine and no one had two doses.