SACRAMENTO - Schoolchildren in California will be required to be vaccinated unless there is a medical reason not to do so, under a sweeping Bill approved by the State Assembly.
The measure, approved on Thursday, would end exemptions for personal or religious reasons, routinely requested by parents opposed to vaccines.
The legislation would make California the largest state by far with such requirements for childhood vaccinations as it joins West Virginia and Mississippi, which have had similar laws for years.
Public health officials hope other states will follow California's lead, though similar measures in some legislatures have been defeated this year.
"We hope and expect we will be a model to get us back to where we should be, which is that cases of measles and other preventable diseases do not need to be something we live with," said State Senator Richard Pan, a paediatrician who wrote the Bill.
Despite overwhelming evidence that vaccines are an essential public health measure, the number of unvaccinated children in California has been rising, partly because personal or religious exemptions have been easy to obtain. Parents who decline vaccines for their children and take heart from the fact that most other children are protected have helped create pockets in particular schools and communities where the overall immunity level is dangerously low, doctors said.
The measure has become one of the most closely watched and divisive in the Capitol this year, with weeks of emotional debates and hundreds of families who oppose vaccines filling the halls, together with their children.
The Senate approved the Bill this year, but will need to vote again to include amendments.
Doctors overwhelmingly recommend childhood vaccines - which have been credited with the elimination or near elimination of diseases like measles, mumps and rubella - and many paediatricians will not accept families who resist vaccines into their practices.
Medical studies purporting to show a link between vaccines and autism have been discredited or retracted, yet some parents cling to them as evidence that their children should not get the shots.
But if too many people in a given community are not vaccinated, doctors say, the "herd immunity" factor that protects vulnerable people and others from these diseases breaks down.
Under the Bill, families who do not want their children to receive vaccines for a non-medical reason would have to home-school their children. Children who are currently in school without vaccines could remain, though they would be expected to show proof of vaccination when they enter kindergarten and seventh grade.
NEW YORK TIMES