MMR vaccines are safe and effective, but fewer children are getting them. Measles and mumps are viral diseases so rare that fewer than one in 40,000 Americans catch either of them in a given year. Getting rubella is less likely than getting struck by lightning.
But as recently as the 1960s, measles sickened half a million people in the U.S. annually and killed hundreds. Mumps was a leading cause of deafness in children and rubella sickened thousands of pregnant women, causing many to miscarry or to deliver infants with birth defects. Measles, mumps and rubella vaccines introduced in the 1960s slashed infection rates. All 50 states require children to receive a combined MMR vaccine before starting school.