Brown, a Democrat, issued a signing statement just one day after lawmakers sent him the bill to strike California's personal belief exemption for immunizations, a move that requires nearly all public schoolchildren to be vaccinated. The bill takes effect next year.
"The science is clear that vaccines dramatically protect children against a number of infectious and dangerous diseases," Brown wrote. "While it's true that no medical intervention is without risk, the evidence shows that immunization powerfully benefits and protects the community."
California joins Mississippi and West Virginia as the only states with such strict requirements.
Democratic Sens. Richard Pan of Sacramento and Ben Allen of Santa Monica introduced the measure after the outbreak at the theme park in December infected over 100 people in the U.S. and Mexico.
The bill likely would be successful in increasing immunization rates and stopping the spread of disease, pediatric doctors said Monday after the state Senate sent the legislation to the governor.
Bill supporters, including doctors, hospital representatives and health advocates, celebrated at an elementary school Tuesday. Lawmakers held babies, declaring the public would be better protected as a result of the bill.
"The science is clear," Pan said. "Californians have spoken. The governor and the Legislature have spoken. No more preventable contagions. No more outbreaks. No more hospitalizations. No more deaths. And no more fear."
Opponents of the requirement have vowed to pursue legal options to block the mandate.
Kimberly McCauley, a Sacramento resident with a 23-month-old daughter, was among a small group of parents holding vigil at the Capitol when they learned of Brown's signing Tuesday morning.
McCauley's eyes filled with tears.
"She will go to school. And then, when she is denied at kindergarten, I will sue," she said.
Allen said he is confident the new law would withstand a legal challenge.
"Similar laws have passed muster over and over again in other states," he said.
Medical exemptions would still be granted to children with serious health issues. Children whose parents refuse vaccination can try to obtain a medical exemption or be homeschooled. The measure applies to public and private schools, as well as day care facilities.
The bill has seen heated opposition from parents who have come by the thousands to protest at the Capitol in recent weeks. The topic has drawn such acidic debate that the authors received threats and were placed under extra security.
A recall effort was even launched against at least two lawmakers who supported the proposal.
Opponents assert that the state is eliminating informed consent and trampling on parental rights. Similar legislation was dropped in Oregon earlier this year because opposition was so fierce.
Despite fervent pushback, the bill passed with bipartisan support.
Brown on Tuesday credited both supporters and opponents with "expressing their positions with eloquence and sincerity."
He said after considerable debate, the Legislature explicitly provided an exception that makes it easier to obtain medical exemptions. SB277 was amended to allow doctors to use a family's medical history as an evaluating factor.
The authors also agreed to establish a grandfather clause, allowing students who currently claim a personal belief exemption to maintain it until their next vaccine checkpoint. Checkpoints occur in kindergarten and seventh grade.