SACRAMENTO, Calif. (AP) — Gov. Jerry Brown wasted no time Tuesday in signing a contentious California bill to impose one of the strictest school vaccination laws in the country following an outbreak of measles at Disneyland late last year.

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 school children 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.

Medical exemptions would still be granted to children with serious health issues. 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 thousand to protest at the Capitol in recent weeks. The topic has drawn such acidic debate that the authors have been added under extra security and a recall effort has been 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 both the California Legislature with bipartisan support.

Brown said he was able to support the measure because the authors agreed to make 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.

Children whose parents refuse vaccination can try to obtain a medical exemption or be homeschooled.

Copyright 2015 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.