The vaccine is the only way to prevent measles, but it also prevents other illnesses. The other "M" stands for mumps, and the "R" stands for rubella. Children can also get an MMRV vaccine, which adds protection against varicella, better known as chickenpox.

For those who were vaccinated for measles many decades ago, there’s a chance the protection has worn off by now. Here's how to determine whether you need a booster.