It’s always frustrating to run up against a bureaucracy wielding a policy that may have a sound grounding, but which is being misapplied. Such was the case this week with a local toddler diagnosed with measles.

As has lately received much attention, after years spent under the impression that measles had been eradicated in the United States, the country has been seeing a relative explosion of cases over the past several years, mainly attributable to misinformation campaigns regarding the safety and effectiveness of the measles, mumps and rubella vaccine. The vaccine is as safe as any such treatment, and very effective. But far too many Americans have been refusing to vaccinate their children, in many cases citing a decades-old discredited and retracted study by British researchers, along with anecdotal evidence propagated through social media, linking the vaccine to autism.

Because of the reach of a few celebrities, the appeal of conspiracy theories and the dynamic whereby many Americans (and others) simply don’t trust what anyone “in authority” says, measles outbreaks have been occurring all over the country this year. Many came about because people who hadn’t been vaccinated visited countries where such vaccinations are less common. When they returned, they spread the disease to others who had eschewed the vaccine, and so on.

This is how disease spreads — or, to be more accurate, the opposite is how it’s contained. When virtually everyone in a population is inoculated, the disease has nowhere to go, and dies out. But the higher percentage who choose not to be protected, the better chance one sick person can become two, then three, and so on.

So, it matters that misinformation about the efficacy of vaccines abounds. The more people duped into choosing not to inoculate their children, the worse the outbreaks stand to be. Even those vaccinated can become sick with the illness, as the vaccine is 97 percent effective. And, importantly, it takes up to three weeks for the vaccine to work, so someone vaccinated very recently can still contract — and spread — the disease.

Enter the N.H. Department of Health and Human Services’ Division of Public Health Services. The division announced Sunday that a child who spent time in Keene had been diagnosed with measles. Because measles is very contagious, the state also noted three public places the child had been before the diagnosis. That was good, because it gave a heads-up to anyone whose children were also in those places at the specified times — especially parents whose children haven’t been vaccinated against measles.

But asked whether the affected child had been vaccinated, the state then dropped the ball, falling back on a policy against giving out any information about specific cases. In essence, the state epidemiologist refused to give out a fact that, since the child wasn’t identified, wouldn’t breach anyone’s privacy, but could have armed the public with better information about the situation.

Immediately after the story was published, The Sentinel’s Facebook page became a hotbed of argument over whether the measles vaccine can actually expose others to the disease. One reader loaded a string of anti-vaccination — as if putting your argument into a bite-sized package lends it credence — while others, weirdly, seemed eager to link the case to immigration.

Things got more confusing after a source speaking for the family mistakenly gave out wrong information regarding the child’s vaccination status. At that point, it was even more important for the health department to step up and correct the record. No dice. Policy is, after all, policy, even when it does a disservice to the public. A spokesman says state law forbids divulging information about an individual’s health record — except when the department feels it’s necessary to the public’s health.

When and whether the child was vaccinated — reliable information obtained since indicates the girl was vaccinated 10 days before the state’s initial warning — really doesn’t change the seriousness of the case for those potentially exposed to the measles. But the social media arguments made clear that the lack of information helped make possible the spread of more misinformation and confusion regarding how effective vaccines are and why they work.

Protecting the medical privacy of patients is certainly a priority for any medical worker or public official. But when knowing a little more about a public health situation would be beneficial, and the information in question doesn’t violate that privacy, the policy ought to be to divulge as much as possible.