The re-emergence of some vaccine-preventable diseases has prompted the California legislature to consider a bill that would make it more difficult for parents to opt out of vaccinating their kids.

The legislation would require that parents get counseling from a doctor before opting out of immunizations for their children.

Last year, the United States saw its highest number of reported measles cases in 15 years, even though the disease was eliminated from the country in 2000, according to the Centers for Disease Control and Prevention.

One theory behind this rise, according to Dr. Richard Pan, the state assemblyman who introduced the bill, is that the recent trend away from immunizing children.