"Like all biological products, you can never say anything is 100 percent safe," explained Dr. William Schaffner, professor of preventive medicine at Vanderbilt University. "But after millions of doses given around the world, I can tell you that adverse events are extremely rare."
One person in six reports having a fever within a week of being given a measles shot, according to the U.S. Centers for Disease Control and Prevention. About 5 percent of people experience a mild rash and about 1 percent of people notice some swelling in their glands.
A severe allergy to the shots occurs less than once in a million doses, according to agency statistics. And autism, coma or brain damage as a result of the vaccine is so extraordinarily rare, Schaffner said, it is hard to pinpoint immunization as the true cause.
The American Academy of Pediatrics also affirmed the importance of vaccines, along with their relatively low risk of harm. In a statement on Monday, the group stressed that the MMR vaccine for measles, mumps and rubella is one of the safest and most effective vaccines given, and strongly urged parents to stick to the vaccine schedule recommended by the CDC.
"While it is best to get the vaccine as soon as your child reaches the recommended age, it is never too late to get your children caught up so they can receive the vaccine and be fully protected," the academy said its statement.
The group also stressed that the dangers of measles are real. Before the vaccine was widely in use, up to 500 children died from the disease each year, said Dr. Richard Besser, ABC News chief health and medical editor.
It is an unfortunate coincidence that vaccines are usually given right around the same time a child is typically flagged for autistic symptoms, Schaffner said.
"It's often difficult to grasp that just because A comes before B does not mean that A is the cause of B," he said.
But Schaffner also acknowledged that vaccinations have become such an emotional issue in this country that all the research and statistics in the world won't sway the opinion of some people.
"As a physician you have to move past it and do your best to be kind and attentive to the needs of the parents and child," he said.