Dr. Charles Goodman vaccinates 1-year-old Cameron Fierro against Hepatitis A after administering a measles-mumps-rubella vaccine (MMR) at his practice in Northridge, Calif. in 2015.

(AP Photo/Damian Dovarganes)

Colorado's low childhood vaccination rate worries Gov. Jared Polis. He told us this week he's "elevating" the issue. But he also said he's wary of any moves by the legislature to make vaccination exemptions harder to come by.

"The minute you try to have the government forcing anybody to do something with their kids, you're going to create distrust of vaccinations, which is already a problem," he said. "We want to go the other way."

The issue is important because immunizations are a price of entry into a state's public education system-- to prevent the spread of disease.

In Colorado, parents can exempt their kids from vaccinations for medical, religious, and personal reasons. Some states only allow medical exemptions, others also allow religious exemptions. According to Dr. Jana Shaw, who specializes in pediatric infectious diseases at SUNY Upstate Medical University in Syracuse, New York, Colorado's online exemption request form is a "particularly easy one."

But, as Polis contends, do more generous exemptions lead to higher vaccination rates? No, Shaw said. The opposite.

"The easier you make it for parents to exempt their children from vaccination, the higher the exemption rates, the greater the risk of measles or pertussis -- whooping cough," said Shaw. "States that permit both religious and philosophical -- personal -- exemptions are states that will have higher exemption rates, and they will also have lower immunization coverage."

"That's concerning because we know that the stricter the immunization law, the better the immunization coverage at the state level," Shaw said, adding that her findings match the work of other researchers. "Those findings are important because, as you know, we have seen erosions of vaccination coverage and community immunity that has led to breakthrough in vaccine-preventable infections such as measles most recently."

Along with comparing data among states, Shaw also said that in states with more exemptions, research has found that at the community level, the unprotected rate among children can be highly concentrated -- between 50-100 percent in some cases. "So the problem is somewhat masked at the state level, and is bigger as you zoom in on communities," she said. "They're clustered" in pockets.

What about the parents who say their own child has been vaccinated, so what's the problem with someone else making a different decision?

"In general that is true: If your child is vaccinated, your child has a very low risk of acquiring vaccine-preventable infections and getting really sick from it. So full vaccination is the safest mode of protection," Shaw said. "However, depending on the age of the child, protection from infection can wane over time."

That means that people who have been vaccinated and might be older, or who might have received a less-effective dose of vaccine, could still contract an infection.

Colorado Gov. Polis said he wants Coloradans to see "good science" on the question of vaccination, and Shaw said research supports that as an effective approach.

"Education is a key to helping parents understand the importance and benefits of vaccination, not only to their own children, but to the people around them. So education should lead the way, but that alone is not sufficient to protect the public," Shaw said.