Only 48.1 percent of students at Waldorf School of Bend last year were fully immunized. At Westside Village it was 35.4 percent, and at Amity Creek Elementary only 33.9.

Those numbers are far below whats needed to provide so-called herd immunity, leaving students and staff vulnerable to outbreaks of diseases from which modern medicine can protect us.

Thats the result of well-intentioned but mistaken parents taking advantage of a far too lax state policy for exemptions.

Despite overwhelming scientific evidence to the contrary, some parents think immunizations are more dangerous than disease. But even if were willing to concede that they have a right to refuse treatment for their own children, the growing numbers of unimmunized children are creating a new threat to others.

Weve all heard plenty about the immunization controversy, but the growing risk posed by the loss of herd immunity is less well understood.

And now we have evidence that its a big potential right here in our own community.

As reporter Markian Hawryluk reported in Thursdays Bulletin Health section, west-side Bend schools Waldorf, Westside and Amity Creek have the highest numbers, but theres plenty to worry about in other area schools as well.

The risk is not just a theory.

When herd immunity is at work, the fact that most people in a group are immunized protects the few who are not. In addition to those who choose not to be immunized, others cant because of medical issues, or arent because their vaccines were only partly effective.

When immunization rates drop, it opens the door for an infectious disease to take hold.

Measles is so contagious that unimmunized people have a 90 percent chance of contracting the disease when exposed to it. If 10 susceptible people are in an elevator with someone who has measles, nine of them will get measles, according to the website of the Vaccine Education Center at the Childrens Hospital of Philadelphia. And the virus could remain in the air for up to two hours, potentially infecting any other susceptible people who enter the elevator-infected environment. Its easy to see how a school setting could replicate that elevator.

And cases of measles have been rising including cases in Hood River and Vancouver, Wash. often started by an international traveler.

If parents cant be convinced to do the right thing, then the state must step in to protect all of us. Its time to look at ways to tighten the now extremely relaxed procedure for claiming a religious exemption to state immunization mandates.

Some states are moving toward making the exemption process more rigorous. In Washington, parents must now have a doctors signature, thus forcing them to have an informed discussion about the benefits and risks of vaccination. Oregon is focused on education, with a new website for parents (www.healthoregon.org/imm).

Thats not enough.

As Dr. Paul Cieslak, Oregons communicable disease program manager said, One of these days were going to get a case in one of those settings and its going to spread like wildfire.

The state has a responsibility to respond before that wildfire gets started.