Parents, teachers and health officials surely hope today that a mini-outbreak of whooping cough will be contained at the three young Bend students who already have fallen ill. Good health may be a matter of luck, however, given the high percentage of parents in this area who refuse to have their children vaccinated against childhood diseases.

The Centers for Disease Control puts Oregon at the top of the list for states with large numbers of unimmunized children, according to the Lund Report, a website that reports on health in the state. Worse, the number of children whose parents seek exemptions continues to grow.

That matters because as fewer children are vaccinated, all children are more at risk for catching genuinely dangerous childhood diseases. That’s because the entire group is at risk of losing herd immunity — in which such a large percentage are vaccinated that disease cannot find a toehold. Children who cannot be vaccinated for medical reasons are in particular danger when herd immunity is lost.

Consider: According to a 2011 article in The Bulletin, between 92 and 94 percent of youngsters in a given population must be vaccinated if there is to be herd immunity against whooping cough, or pertussis. Yet some schools in the area, both public and private, reported much lower vaccination rates, just over 50 percent in one school and between two-thirds and three-quarters in several others. In those schools, herd immunity is long gone.

The three youngsters who became ill recently were connected to one another in some way, according to Deschutes County officials, though they apparently do not all attend the same school. Those facts, combined with the highly contagious nature of whooping cough and the risk of death it presents to newborns, should give parents in all Bend-area schools pause.

Are their own children at risk? If they’re not vaccinated, and children under 2 months old cannot be vaccinated against pertussis, the answer may be yes.

We cannot imagine the parent who would willingly endanger another family’s child, yet that’s just what parents do when they refuse to vaccinate their own children. Perhaps they do not recognize how their own exercise of freedom can intrude on others. If not, it’s time they did.