The Senate reaffirmed the bill striking California's personal belief exemption for immunizations on a 24-14 vote. Mississippi and West Virginia are the only two states with such strict requirements in place.
Democratic Gov. Jerry Brown has not said if he would sign it. Although the bill passed the Senate and the Assembly with bipartisan support, it did not pass with a two-thirds threshold that would be needed to override a governor's veto.
Parents opposed to the bill vowed to take legal action even though the issue has been upheld in court, including by the Supreme Court.
"I will sue to put my child in school," said Jude Tovatt of Roseville and the parent of an 8-year-old child. "I will not run from the state that is our home."
Other parents cheered the legislative vote and immediately turned their attention to swaying Brown.
"I know that he is very pro-science and that's really what this bill comes down to: leadership in public health, and supporting evidence-based science," said Hannah Henry, mother of four from Napa who started Vaccinate California, a parental group in support of the bill.
Brown has 12 days to decide the bill. The governor's office immediately began receiving petitions from both sides.
"The governor believes that vaccinations are profoundly important and a major public health benefit, and any bill that reaches his desk will be closely considered," governor's spokesman Evan Westrup has repeated in recent days.
Democratic Sens. Richard Pan of Sacramento and Ben Allen of Santa Monica introduced the measure after the outbreak of measles at Disneyland in December infected over 100 people in the U.S. and Mexico. It applies to public and private schools, as well as day care facilities.
"The science remains unequivocal that vaccines are safe, that vaccines save lives," Pan said.
If the bill becomes law, 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. Otherwise, school-age children who currently claim a personal belief exemption will need to get fully vaccinated by kindergarten and seventh grade, the state's two vaccine checkpoints.
The measure has prompted the most heated legislative debate of the year with thousands of parents taking to social media and flooding the Capitol in recent weeks to oppose the bill at legislative hearings. They and some lawmakers say that the state is eliminating informed consent and trampling on parental rights.
Sen. Joel Anderson, R-Alpine, said the measure should have had provisions in place for parents who opt to take their children out of school, rather than get them vaccinated.
"It doesn't provide that the districts in any way are financially responsible for those students who are denied a public education," said Anderson.
The Senate voted Monday on changes made to the bill in the Assembly that make it easier to obtain medical exemptions. The amendment would allow doctors to use a family's medical history as an evaluating factor.
The bill 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.