A proposed bill would make it harder for Colorado parents to opt their children out of immunizations for personal or religious reasons by requiring an in-person visit to their local health department to get a signature on the exemption form.

The bill, introduced by Rep. Kyle Mullica, a Democrat from Northglenn, comes as measles outbreaks around the country grab headlines. It aims to boost Colorado’s lower-than-average childhood vaccination rates by reducing the number of parents who skip shots for their children.

But the bill doesn’t go as far as banning personal belief or religious exemptions, a plan rumored to be in the works earlier this year and that Gov. Jared Polis was expected to oppose.

In Colorado, 89 percent of kindergarteners were vaccinated against mumps, measles and rubella last year, compared with a national median of 94 percent. While Colorado law requires proof of immunizations for enrollment in child care centers and K-12 schools, parents are allowed to opt out for medical, religious or “personal belief” reasons.

Some parents skip shots because they fear the possibility of alarming side effects, don’t think vaccines work, or believe their children will develop stronger immune systems if they get diseases like measles or chicken pox. About 4.5 percent of Colorado kindergarteners didn’t get shots because of religious or personal belief exemptions last year, according to estimates from the Centers for Disease Control and Prevention.

Public health officials have long been frustrated by Colorado’s lenient exemption rules, worrying that some parents claimed personal belief exemptions not because they have deep-seated convictions about vaccines, but because it’s been far easier to claim the exemption than deal with the logistics of getting kids immunized.

Such concerns prompted a five-year push to align Colorado’s immunization policies more closely with those in states where a larger share of children get vaccinated. Efforts started in 2014 with a bill that required schools to provide immunization and exemption rates to the public.

The original version of that bill — like the one this year — would have made it harder for parents to claim personal belief exemptions. But instead of mandating a health department visit and signature, it would have required that parents be briefed by a medical professional on the pros and cons of immunizations or complete an online education session. (A similar model has been used in Oregon since 2013.) That provision was ultimately stripped out of the bill.

Later, additional changes came online, including a statewide school-by-school database of immunization and exemption rates, and a rule requiring parents to submit non-medical exemptions to their child’s school every year, not just once as was allowed previously.

The current bill, besides requiring parents to submit their non-medical exemption form for a signature during an in-person health department visit, would require parents to use a state-designated exemption form. Currently, parents can write a letter in lieu of using an official form.

Under Mullica’s bill, parents would have to get health department signatures every year, but could go through an online process after that initial in-person visit.

Stephanie Wasserman, executive director of the Colorado Children’s Immunization Coalition, said the bill is similar to Michigan law, where parents seeking non-medical exemptions also have to visit their local health departments to get an official signature on their exemption form. (In Michigan, unlike under Colorado’s proposal, parents must have a counseling session on immunizations at the health department.)

“We really think this is a very common-sense approach and it gets us to the outcome that I think most families in Colorado are supportive of,” she said.