California Gov. Jerry Brown on Tuesday signed legislation that would ban personal belief and religious exemptions to day care and school vaccination requirements.

SB 277 requires all children entering day care, kindergarten or 7th grade to be vaccinated, although the legislature included a specific exemption if a child's physician concludes that immunization is not recommended for reasons including family medical history.

"The science is clear that vaccines dramatically protect children against a number of infectious and dangerous diseases," Brown wrote in a signing message Tuesday. "While it's true that no medical intervention is without risk, the evidence shows that immunization powerfully benefits and protects the community." (You can read the governor's full statement below).

State Senators Richard Pan (D-Sacramento) and Ben Allen (D-Santa Monica) introduced SB 277 earlier this year following the measles outbreak that began in December at the Disney theme parks in Anaheim.

Public health officials said a significant number of those who caught the measles in the outbreak were unvaccinated.

The bill's authors said it was necessary to advance the effort to achieve herd immunity throughout the state. Herd immunity refers to the achievement of a high enough level of vaccination in a population to protect everyone, including those who cannot be immunized for medical reasons.

From a statewide perspective, California has achieved herd immunity, but there are pockets of resistance to vaccination — in some rural and wealthy enclaves — that have left certain communities well short of that goal.

Sen. Pan, speaking on KPCC's AirTalk on Tuesday, said he was pleased that Brown had "listened to the science, listened to the facts about vaccination." Brown, he said, has "taken a very important step in assuring we stop the erosion of community immunity in California and that we prevent diseases that should stay in the history books."

Pan, who is also a pediatrician, said he was confident that the legislation would stand up against any forthcoming legal challenges.

"The bill has been thoroughly vetted ... across four different policy committee hearings, as well as two floor debates in the state Legislature, including review by the Senate Judiciary Committee," Pan said. "The courts have repeatedly ruled that you do not have the right to spread a communicable disease, and that government has a role in protecting the public from these diseases. So I feel strongly that this bill is sound, it will withstand the legal and constitutional scrutiny."

Christina Hildebrand, founder and president of Voice for Choice, a group which has opposed the legislation, said on AirTalk that while the new law will allow doctors to grant exemptions at parents' request, she is concerned about the pressure that could be put on doctors who do so.

"Will there be doctors that give medical exemptions for medical reasons such as genetic disorders or family history? There will be," Hildebrand said. "But my fear is that those doctors who do that will be far and few between. They usually do not take insurance, so that you have to have money in order to go that route. And, if they do do it — if they have a stack of 100, 200, 300 medical exemptions on their records — what does that do ... when the licensing board comes down on them or something like that?"

Hildebrand said her group will attempt to overturn the law through a ballot referendum and a court challenge.

The new law's opponents have also argued that it violates the state constitution's guarantee of education for every child by denying parents the right to send their kids to school, asserting that some parents who might not want to fully vaccinate their kids might not be able to afford to home-school them. The ACLU of California voiced similar concerns during the debate over SB 277, although the civil rights group said it was neutral on the measure.

In response to the criticism, Pan amended the bill to allow those who opt out of vaccination to set up multiple-family home schools, and to home-school their children using a public school independent study program.

While state law requires children be immunized upon entering day care, kindergarten and 7th grade, the new law grandfathers in children who are already enrolled in day care or school with a personal belief exemption. So for example, if a child whose parents obtained a personal belief exemption is in 1st grade, he will not need to get up to date on his vaccinations until he enters 7th grade.

The legislation touched off an intense political battle in Sacramento. People opposed to all vaccinations joined forces with those who wanted the flexibility to moderate the recommended vaccination schedule to fight the bill. Hundreds of parents crowded into committee hearings and held rallies in the Capitol.

Sen. Pan's staff said he received death threats and images comparing him to Adolf Hitler circulated online.

With Brown's signing of the bill, California becomes the 32nd state not to allow a personal belief exemption (Washington, D.C., also does not allow this exemption) and just the third state — along with West Virginia and Mississippi — to bar a religious exemption, even though no major religion opposes immunization.

One of the strongest supporters of the legislation, Carl Krawitt, said on KPCC's Take Two that he was pleased with the passage and signing of the bill.

"We're pleased that our message resonated with our legislators, and that they legislated from solid evidence and not some fear," Krawitt said. "They have a duty to protect our community, and Gov. Brown has validated that duty by signing this [into] law, so we're extremely pleased."

Krawitt got involved in the issue out of concern for his son, Rhett, who is now 7 and has leukemia. When Rhett was 6 and undergoing chemotherapy, he couldn't receive vaccines because he had a compromised immune system.

"When the measles outbreak hit, [school officials] told us that he wouldn't be able to go to school if measles hit his classroom," Krawitt said. "And we felt, Why should he suffer and not be able to go to school?"

Rhett testified before the California Senate Education Committee earlier this year, imploring lawmakers to pass SB 277: "Thank you for making sure that kids like me don't get sick at school," Rhett said.

Governor Brown's statement on signing SB 277

Reaction to vaccination law

This story has been updated.