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Are 'opt-out' parents and unvaxxed kids a health threat?

More and more parents are opting out of vaccinations for their kids.

In eight states now, more than 1 in 20 public school kindergartners aren't getting all the vaccines required for attendance, an Associated Press analysis found. That growing trend among parents seeking vaccine exemptions has health officials worried about outbreaks of diseases that once were all but stamped out.

"Study after study after study has shown that vaccines are safe, so why are so many parents still convinced it's not right for their children?" TODAY's Matt Lauer asked NBC Chief Medical Editor Dr. Nancy Snyderman.

Snyderman said it's not a lack of resources or education. The "profile" of the non-vax parent is middle-class, college educated and web-savvy, she said. There is also a new generation of parents in their 30s and 40s who "have no memory of polio, whooping cough and measles."

The problem is, there have been deadly outbreaks of measles and whooping cough in recent years. In California last year, 24 children died of whooping cough.

Secondly, Snyderman said, parents who opt out of vaccines put others risk. Infants who are too young for vaccines, people undergoing chemotherapy, anyone with a weak immune system could catch a disease from an unvaccinated child: "An un-immunized child is a walking Typhoid Mary who can put any of those immune-compromised people in an early grave," Snyderman said. "I personally think it is selfish not to think of that."

What do you think? Are parents who opt out of vaccines being reckless, or cautious?