No one fears a comeback more than those who are unable to get vaccinated, like 7-year-old Ben Bredesen.
More -- 'Conscientious objectors' forgo vaccines for their kids
Bredesen's immune system was left compromised as he underwent chemotherapy for leukemia.
But it wasn't the leukemia doctors were worried about -- it was measles.
His mother, Laura Bredesen, says, "They didn't mince words when they told us how critical it was if he came down with measles."
While undergoing a spinal tap, Ben ended up in the same ward as another child who later developed measles. His parents had to quarantine Ben for 21 days and feared the worst.
Kids like Ben are why doctors talk about so-called 'herd immunity,' vaccinating healthy kids to protect children like Ben who are too sick to vaccinate.
But Minnesota is one of 22 states that allows 'conscientious objector' parents to skip vaccinations for non-medical reasons.
Christine Abel of Vaccine Awareness Minnesota says, "Yes, on occasion someone gets measles and dies. But you can't base your life on a few people."
"You have to ask what's wrong with them," she continues. "Why did they die when most people don't die."
But as an outbreak that began in December at Disneyland has led to more than 100 cases, in 14 states, now even politicians are jumping in.
President Barack Obama says, "I understand that there are families that in some cases are concerned about the effect of vaccinations. The science is pretty indisputable."
On a slightly different note, New Jersey Gov. Chris Christie says, "I also understand parents need to have some measure of choice in things as well. So that's the battle that the government has to decide."
Ben Bredesen never did develop measles, and his immune system is healthy enough now that he's had his measles shot. But his mother can't help thinking about all those kids who don't have that choice.
"If there [is] just a small pocket of people around those individuals it threatens their lives," Laura says.
The last measles outbreak in Minnesota was four years ago. Most of the 21 children who came down with measles were unvaccinated because of parental concerns. Seven children were infants who were too young to receive the vaccine.
You can read Laura's Voices for Vaccines blog about what lessons she's drawn from Ben's experiences here.