Several state legislatures are debating vaccine-related measures as dozens of people have fallen ill from a measles outbreak that started at Disneyland in December and spread beyond the theme park. Here is a look at some of the legislation around the country:
Three California lawmakers, all Democrats, introduced legislation this week that would require parents to vaccinate their children before they enter school unless the child cannot be immunized because of a medical condition.
Parents would no longer be able to cite personal beliefs or religious reasons to send unvaccinated children to private and public schools. Mississippi and West Virginia are the only other states with such strict vaccine rules, although the California bill's lead author said he would consider including a religious exemption.
California is among 20 states that allow for personal belief exemptions and 48 that allow for religious exemptions, according to the National Conference of State Legislatures.
A bill introduced by a Democratic lawmaker would eliminate the philosophical exemption that allows parents to skip vaccinations for their children. A separate proposal backed by Democrats aims to make getting exemptions more difficult.
That bill would require parents to consult with a medical professional about the risks and benefits of vaccines and obtain a signed form if they wish to opt out for non-medical reasons.
Another measure, introduced by Republicans, would create a vaccine safety office in Maine's Center for Disease Control and Prevention that would offer parents guidance on the risks of vaccines. Committee hearings have not yet been held on the bills.
A statewide rule change that took effect Jan. 1 requires parents wanting a philosophical or religious waiver for childhood vaccinations to first be educated by a local health department about the risks. Previously, parents could submit a vaccination waiver to a day care center or school without being briefed by a health expert. Michigan has one of the highest vaccination waiver rates in the U.S.
The rule change was pushed by the administration of Gov. Rick Snyder, a Republican, and approved by lawmakers.
A bill before Minnesota lawmakers would retain existing vaccine exemptions for medical reasons or in cases of personal belief. But parents or guardians of children claiming the personal-belief exemption would have to consult with a doctor about the risks associated with remaining unvaccinated. They also would have to acknowledge that their children could be barred from school or a child-care facility in the event of an outbreak. The bill has yet to be scheduled for a hearing.
Under a bill that awaits a full legislative debate, the Mississippi State Department of Health would lose its role in deciding whether a child can skip or delay a vaccination that is otherwise mandatory in the state. Instead, it would allow a physician to grant a patient's vaccine exemption for medical reasons, without seeking the department's approval.
The U.S. Centers for Disease Control and Prevention says Mississippi had the largest percentage of kindergartners in public and private schools who have been vaccinated against diseases for the 2013-14 school year, a rate of 99.7 percent.
A Republican lawmaker has added an amendment to an immunization bill that would allow for a greater number of parents to opt out of vaccinations altogether.
The amended version would allow parents to forgo vaccinations for their children based on "personal beliefs." Montana law already allows exemptions for medical reasons and religious beliefs. It passed the House on a 95-4 vote this week.
Republican Rep. Greg Hertz, who added the amendment, said he did so to extend rights to parents who are not religious, giving them a route to opt out of vaccinations.
The Democratic sponsor of the bill, Rep. Margie MacDonald, said she plans to ask a Senate committee to remove the amendment. Her original bill sought to add chicken pox and whooping cough to the list of required childhood vaccines.
Legislation introduced in New York's state Senate and Assembly would widen existing exemptions to vaccine mandates by creating a "philosophical" exemption for those whose opposition to immunizations is not based on religious reasons.
Currently, children must be vaccinated before attending school unless they obtain a waiver stating that they cannot receive immunizations for medical or religious reasons. But the bill's supporters say many parents might have general concerns about vaccines that are not tied to religious doctrine.
Similar bills have been introduced in past years and have not received a vote.
A bill scheduled for a vote in the state Senate would reauthorize schools and day care providers to be able to access records in the state's immunization registry without parental consent, unless there is a signed refusal for the release of the information in the patient's medical record.
Federal rule changes forced the state in August to allow schools and day care services to access the registry only if they received parental consent, so the state Department of Health brought the proposal forward to restore access.
Privacy advocates in the state Legislature won a victory by securing an amendment to the health department's proposal. It requires providers to tell parents they have the right to stop the immunization information from being shared.
Oregon made it harder for parents to opt out of vaccinations for nonmedical reasons in 2013. That law requires parents to meet with a doctor or watch an informational video before they can reject vaccines for a child entering kindergarten. A bill proposed this year would expand the requirement to all children, including those already in school. A hearing on the bill has yet to be scheduled.
The CDC reported that Oregon had the nation's highest rate of nonmedical vaccine exemptions during the 2012-13 school year.
A group of lawmakers this week announced plans to introduce legislation that would eliminate the philosophical exemption for parents who do not want their children immunized. A similar effort failed three years ago.
A group advocating for parental rights, the Vermont Coalition for Vaccine Choice, issued an "urgent action alert" that urged its members to help stop the proposal.
Gov. Peter Shumlin, a Democrat, said he believes the philosophical exemption should be left as it is. Vermont is in the top three states in the country for people taking the exemption.
Gov. Jay Inslee signaled his support for a House bill introduced this week that would remove philosophical opposition as an acceptable reason for parents to avoid vaccinating their school-age children.
Washington allows school vaccination exemptions for medical reasons and personal or religious beliefs. This week, Democratic Rep. June Robinson introduced House Bill 2009, which removes the exemption for personal or philosophical beliefs.
The state law on exemptions was last changed in 2011 to require proof that a parent seeking one had received information from a health care provider about the benefits and risks of vaccinations. People who can show they are a member of a religious group that does not believe in medical treatment can bypass this requirement.
A state Senate committee this week stripped language from a bill that would have allowed parents to claim religious exemptions from childhood vaccinations.
The bill by Republican Sen. Ryan Ferns would have changed that. Parents would have been able to sign affidavits saying certain vaccinations for their children were against their religious beliefs. That language was removed this week.
Associated Press writers Brian Bakst in St. Paul, Minnesota; Lisa Baumann in Helena, Montana; Alanna Durkin in Augusta, Maine; Jonathan Cooper in Salem, Oregon; David Eggert in Lansing, Michigan; David Klepper in Albany, New York; Rachel La Corte in Olympia, Washington; Jonathan Mattise in Charleston, West Virginia; Fenit Nirappil in Sacramento, California; James Nord in Pierre, South Dakota; and Emily Wagster Pettus in Jackson, Mississippi, contributed to this report.