California lawmakers have put forward legislation requiring parents to vaccinate all school children unless a child is deemed to be in danger due to a pre-existing medical condition. If passed, California would join only two other states with such stringent restrictions.

Parents could no longer cite personal beliefs or religious reasons to send unvaccinated children to private and public schools under the proposal introduced Wednesday after dozens of people fell ill from a measles outbreak that started in the state’s Disneyland resort. Indeed the only exemptions would be for children who could be at risk due to allergic responses or a weakened immune system caused by serious illness.

Mississippi and West Virginia are the only other states with such strict vaccine rules, though the California bill's chief author said he would consider including a religious exemption — a move likely to undermine efforts to protect children in the states from preventable diseases.

"People are starting to realize, ‘I'm vulnerable, my children are vulnerable,'" said Sen. Richard Pan, a Democratic pediatrician from Sacramento. "We should not wait for more children to sicken or die before we act."

Childhood vaccine has become an emotionally charged topic amid a measles outbreak that has sickened more than 100 people across the U.S. and in Mexico. No deaths have been reported.

According to the National Conference of State Legislatures, California is among 20 states that allow for personal belief exemptions and 48 that allow for religious exemptions.

A Washington state lawmaker introduced a bill Wednesday that would remove the personal belief allowance for an exemption in that state.

Public health officials believe an immunization rate of at least 90 percent is critical to minimizing the potential for a disease outbreak. California's kindergarteners met that threshold at the start of this school year, according to state statistics. Two percent were exempted because of their parents' personal beliefs, and another half a percent were exempted because of their parent's religion.

Less than one-fifth of a percent of all students — about 1,000 — had a medical vaccine exemption that would be preserved under the bill.

Pan, who previously served in the Assembly, was the author of another vaccination bill that took effect last year. It requires parents who don't have their children vaccinated for non-religious reasons to get a note from the doctor's office before enrolling their children in school.

A spokesman for Gov. Jerry Brown, who signed that bill, did not say if the governor would oppose efforts to end exemptions.

"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," spokesman Evan Westrup wrote in an email.

Parents cite a variety of reasons for not immunizing their children: religious values, concerns — widely discredited by the medical community — the shots could cause illness and a belief that allowing children to get sick helps them to build a stronger immune system.

The American Academy of Pediatrics says doctors should bring up the importance of vaccinations during visits but should respect a parent's wishes unless there's a significant risk to the child.

The California bill is also backed by Democratic Assemblywoman Lorena Gonzalez and Democratic Sen. Ben Allen, a former Santa Monica school board member.

Separately on Wednesday, U.S. Sens. Barbara Boxer and Dianne Feinstein called on California's top health official to reconsider the state's policy on vaccine exemptions in light of the measles outbreak.

"We believe there should be no such thing as a philosophical or personal belief exemption, since everyone uses public spaces," the Democratic senators wrote in an open letter.

Measles was declared eliminated in the United States in 2000 after decades of intensive childhood vaccine efforts. But last year the nation had its highest number of measles cases in two decades.

Most people recover from measles within a few weeks, although it can be fatal in some cases.

Wire services