SACRAMENTO — After months of rancorous debate and emotional pleas from parents, a bill that would force most Californians to vaccinate their children cleared its last major legislative hurdle on Thursday.

So now the only question is: Will California’s famously unpredictable governor give the measure his blessing?

Senate Bill 277, which mandates vaccinations for all schoolchildren regardless of their parents’ personal or religious beliefs, passed on a 46-to-31 vote in the state Assembly after an hourlong impassioned debate. That much was expected, as is Monday’s pro forma Senate vote to approve the bill again and send it to Gov. Jerry Brown for his signature.

Many pundits are reluctant to predict what Brown will do.

“The three great mysteries in life are the Holy Trinity, transubstantiation and Jerry Brown’s mind,” said Jack Pitney, a Claremont McKenna College political science professor who has studied Brown’s decades-long political career.

The last time he endorsed a vaccine bill in 2012, the former Jesuit seminarian tweaked it to make it easier for Californians to claim religious exemptions. Will he be tempted to do that again — and water down the current legislation?

“He knows the science. I’ve tracked his statements over the years on various issues, and he is aware of the need for vaccinations — he knows how measles spreads,” Pitney said. “The question is whether he sees this as an issue of religious freedom.”

Controversy around the elimination of the “personal belief exemption” was spurred in California after a measles outbreak started last December at Disneyland.

If enacted into law, California would join only two other states — Mississippi and West Virginia — that permit only medical exemptions as legitimate reasons to sidestep vaccinations.

Hundreds of parents who oppose the legislation have rallied several times at the Capitol, saying the bill violates their parental rights. Other opponents believe that some vaccines are unsafe for some children.

Over the months that SB 277 has journeyed through the state Senate and Assembly, the governor’s staff has repeatedly said that he “believes that vaccinations are profoundly important and a major public health benefit and any bill that reaches his desk will be closely considered.”

Brown supported a tightening of vaccine policy in 2012 when he signed AB 2109, a bill by then-Assemblyman Richard Pan. The Sacramento Democrat, now a senator, also co-authored SB 277.

The 2012 measure required parents who wanted to exempt their children from the shots to meet with a health care professional first. Brown then directed the state Department of Public Health to allow people “whose religious beliefs preclude vaccinations” to avoid requirements to get a health care practitioner’s signature.

But legal experts say Brown had no standing to issue such a directive — and he doesn’t have it now either.

“The governor doesn’t have the authority to make this sort of change on his own. He simply doesn’t,” said Dorit Rubinstein Reiss, a UC Hastings expert on public law. “If someone had taken him to court, that clause could have been ruled unconstitutional.”

Evan Westrup, Brown’s spokesman, responded to that critique by saying: “The weight given to a signing message is a matter for the courts to decide.”

For his part, Pan said he’s had “positive conversations” with the Brown administration about the bill, noting that so far no one has expressed an interest in protecting the religious exemption that’s allowed under current law.

“I’m not going to predict what the governor will do, but we have not heard that that’s an issue he’s raised for this bill,” Pan said.

Besides, this bill is different, said Barbara O’Connor, director emeritus of the Institute for the Study of Politics and Media at Sacramento State. She’s someone who has known Brown since his first stint as governor four decades ago.

Were he to add a religious exemption to this bill, she said, “I think the legislative analyst would say that’s not a minor modification — it changes the totality of the law.

“If you allow people to get a religious exemption,” she said, “then everyone who opposes the bill will get one.”

O’Connor knows Brown’s religious background. “But he is a Jesuit, and Jesuits are different,” she said. “They are not Holy Roller Catholics — they’re intellectual Catholics.”

Dr. Bart Lally, a South Bay gastroenterologist and longtime Catholic childhood and college friend of Brown’s, said he was confident the governor “will do what he thinks is right.”

Proving that lawmakers’ positions on the issue blur party lines, five Democrats voted against the bill, two Republicans — including Assemblywoman Catharine Baker, R-San Ramon — voted for the bill, and three Democrats and one Republican abstained.

Assemblyman Kansen Chu, D-San Jose, was one of the legislators who declined to cast a vote.

“I came to the conclusion that we were exercising too much authority on a problem that does not exist yet,” Chu told this newspaper afterward. He said he based part of his decision on three families from his district who visited him and opposed the bill, saying it would deprive their children the right to attend public school.

“They pretty much convinced me that we didn’t need to take such a drastic approach,” Chu said.

Contact Tracy Seipel at 408-920-5343 and follow her at Twitter.com/taseipel. Contact Jessica Calefati at 916-441-2101 and follow her at Twitter.com/Calefati.