Wall Street Journal reporter Caroline Porter joins me now from Los Angeles with more on this divisive issue.

　　So, put the numbers in perspective. How many kids in the California school system aren't vaccinated?

　　CAROLINE PORTER, WALL STREET JOURNAL: So, it's a small percentage of school children who are not vaccinated. But the concern is that it could be rising. Over the past decade or so, we've seen an increase in parents who are looking at ways to reduce or possibly change the way in which children receive their vaccinations.

　　And the concern is there would be clusters of children where they don't reach what's called herd immunity, where there aren't 95 percent of the population with the required vaccines which would make outbreaks more likely.

　　HARI SREENIVASAN: And where are these clusters or what do we know about them?

　　CAROLINE PORTER: So, the clusters seem to be in places with either high educated population or those without — below the poverty line. So it seems to go either — in a situation where there aren't enough resources or where there are such resources that people are taking their own initiative not to vaccinate.

　　HARI SREENIVASAN: So, if this law gets signed by Governor Brown, does this mean that if you have a — if you want a personal belief exemption, you're going to have to home-school your child?

　　CAROLINE PORTER: Well, that's correct. I mean, basically, that's one of the main concerns that opposers have, is that it's a constitutional right to a free public education in California. So, if I choose not to vaccinate my children, does that mean I have to home-school?

　　And there are a couple of exceptions to that. You can home-school in groups, so families can get together and say, you know, we're going to home-school our children together because they all do not have the same requirements in terms of vaccines.

　　The other option is you can have what's called an independent study in schools. But what that generally means is that you won't be in a classroom with other students by and large.

　　HARI SREENIVASAN: So, if this becomes law, is the opposition ready to sue to try to challenge it?

　　CAROLINE PORTER: So, the opposition has been loud. I mean, in terms of testimony and hearings and protests and petitions, from what I hear, it's been one of the most controversial and acrimonious debates that we've had here in California this legislative session. And talking to different protesters or organizers, what I hear is that they are considering litigation.

　　HARI SREENIVASAN: And where do doctors come down on this? I know some pediatricians' offices will actually refuse to see you in their clinics if you don't vaccinate your child.

　　CAROLINE PORTER: You know, every doctor's going to have a different opinion. But the cosponsor of the bill is a pediatrician himself. And I think that's, you know, one of the main thoughts of his in wanting to put this through is concerns for the population at large and the medical community has had concerns.

　　HARI SREENIVASAN: All right. Caroline Porter of The Wall Street Journal joining us from Los Angeles — thanks so much.

　　CAROLINE PORTER: Thank you.