Two California state senators have introduced legislation that would require California parents to vaccinate their children, unless they can obtain medical exemptions. California currently has a personal belief exemption that lets parents refuse to vaccinate on the basis of personal or religious beliefs.

The bill would end those exemptions and make a medical reason the only option for those seeking exemptions. Mississippi and West Virginia are the only states that currently have laws allowing solely for medical exemptions from vaccination. State Sen. Richard Pan, who is also a pediatrician, and state Sen. Ben Allen introduced the legislation on Thursday.

The omission of a religious exemption could be controversial, however, and Pan told the San Jose Mercury News he was open to discussing such an exemption as the legislation is debated in coming months. In 2014, an immunization law in California went into effect requiring parents seeking exemptions from vaccinating their kindergartners to obtain a signature from a medical professional indicating that the parents had been made aware of the risks of not vaccinating. However, under that law, those seeking exemptions from vaccination on religious grounds did not have to speak with a medical professional first.

Anti-vaccination sentiment in California has risen significantly in recent years, vaccination rates suggest. In 2000, only 0.77 percent of California parents sought vaccination exemptions for their children. In 2014, 2.5 percent did.

California’s overall vaccination rate of 90.7 percent is not so bad, compared to other states. (Ohio, West Virginia and Colorado’s vaccination rates are the lowest, at 86 percent.) But within California, rates vary by county and in some areas of the state, it’s far lower. At least 119 Californians have been infected in a measles outbreak that has infected 162 people in 17 states, with low vaccination rates in certain counties playing a key role in the virus’s spread.