Now, a closer look at an alarming number of measles and mumps outbreaks nationwide. In schools from New York to California, more than 16,000 children entered kindergarten without measles vaccinations.... See More
Now, a closer look at an alarming number of measles and mumps outbreaks nationwide. In schools from New York to California, more than 16,000 children entered kindergarten without measles vaccinations. That's up 15% from last year and double the number from six years ago. Are the outbreaks caused by parents choosing not to have their children vaccinated? Your doctor wouldn't recognize this disease, neither would you. It's measles. I think we weren't talking about measles. Most residents who are training have never seen measles. Reporter: A disease we thought eliminated in the U.S. 51 cases this year in California. Last year? Just four. Measles is on the rise. Dr. Mark sawyer has a negative pressure room in the er at the children's hospital to isolate potential measles cases. This machine cycles air and puts it through a filter to take out the infectious agent. Reporter: He's bracing for more. Because an increasing number of parents won't vaccinate their children, or choose to delay vacces past the recommended ages. We're up to 4.5% of our children at kindergarten age who have not had their vaccines. Reporter: That's a lot of kids. It's getting up there. Reporter: And those kids are from affluent communities like Orange county. Home to this family and their 2-year-old twins who haven't had their measles shots. Your approach to vaccination. Sum it up? What's the risk and the reward? I find it to be very low risk of contracting measles. Reporter: An increasing number of parents believe there's too many shots at once. Their girls have had some vaccines, but their parents are holding off on measles until just before they start kindergarten. They are counting on the fact most kids get the shots, giving protection for the rest. Hillary chambers has something to say to those parents. That's not fair to everybody else. You're relying on everybody else to do it for you. Reporter: Outbreaks occur when travelers bring measles in from other parts of the world where the disease is more common. During a 2008 measles outbreak, Hillary's daughter was exposed to a child who got measles from an unvaccinated child. She was quarantined for 21 days. This incredibly fast moving virus encounters an unvaccinated child in a waiting room. Not this doctor, he won't accept families who don't want vaccines. I'm drawing a line in the sand. Reporter: Isn't it a parent's right to vaccinate their child or not? Would you send your teen out to drive a car without a seat belt? Would you go out on a boating trip with your family and decide who wants to wear life jackets and who doesn't? That's like playing Russian roulette. You don't know if that's the one and a thousand child that's going to die from this illness. Dr. Besser is here, along with Michael specter author of denialism. Dr. Besser, start with you. This is a fascinating dilemma. Two rights, two values here. One, individual rights and the right of the community for public health. So my question to you is, is the public health concerns so overwhelming that parents should be forced to vaccinate their children? Well, you know, I think it is. If you look at the impact -- impacts in public health, there's been nothing that has equalled that of vaccination. The problem we have is that the success of vaccination programs means that no one is seeing these diseases. They don't understand what can happen if we move back. If you want to sent your kid to public schools, no IFS, ands or buts about it, they have to be vaccinated. How do you do that? How you force somebody? I don't think we will be able to force people. That's the problem. I agree with Dr. Besser. But the fact of the matter is, we're not going to be able to force people to stick needles in their kids' arms. We need to do a better job of educating them. Thing -- they think about risk in the wrong way. They think about risks of something happening. They do not think of the risks of what might happen if they don't do this vaccine. They are great and getting greater. You actually -- you would say, you can't go to public school without a vaccine? I think that's right. The Numbers in terms of undervaccination, about 4%, is not very great. Most people are doing the right thing, vaccinating on time. But you have the pockets, some of these schools in San Diego, 20% of the kids are not up to date on their vaccines. That's a ticking time bomb. Give me the profile. Who are the people that are opting out and not vaccinating their kids? I'm sorry to say, they're people who are highly well-educated, live near me in the park slope in Brooklyn, who think that their education status somehow exempts them from these problems that other people have. And infectious diseases are infectious to everyone. Viruss don't choose who to infect. They feel they are smarter than the doctors. I think they feel that the risk is so low it's not worth worrying about, and there are other things to worry about more. They are wrong about that. Just wrong. I ran the training program in San Diego in the hospital we saw, and the residents, the doctors being trained, haven't seen these diseases either. So they're often willing to give into a parent who says I'm worried, I don't want that shot on my child. That's part of the problem. Fascinating. A lot more to talk about in the future. Dr. Besser, Michael, thank you for joining us.
This transcript has been automatically generated and may not be 100% accurate.