Amid one of the largest measles outbreaks in the United States in nearly a decade, anti-vaccine activists are promoting false claims that shots are ineffective in stemming the spread of the virus or that they could cause the disease.

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.