Here’s an interesting fact about diphtheria: When it was still a common illness in 1970s, it was known as “the strangling angel of children.” Here’s a less interesting one: Nearly three decades after its eradication in Spain, it’s back.

This new case comes in the form of a 6-year-old boy, whose parents are watching him “fight for his life” in a Barcelona intensive care unit. Since his diagnosis, eight other children he came in contact with have tested positive for the bacterium that causes the illness.

So why has a disease with a nickname that seems ripped straight from Game of Thrones back in a nation as developed as Spain? Simple: because his parents did not have him vaccinated against it—a decision his parents understandably have come to profoundly regret. Admittedly swayed by the anti-vaccination movement in the U.S., the couple is reportedly “destroyed” and feels “cheated” by the anti-vaxxers.

To date, none of the eight infected children have actually become ill themselves. This may well be because all of them were vaccinated against it. (They are all being given antibiotics and kept in isolation to prevent their developing and spreading the disease anyhow, which is entirely appropriate). But no vaccine is 100 percent effective in everyone.

The incident was met with shock in Spain, where the lack of medicine to treat the illness allegedly forced authorities to send for some in Russia. Now with eight kids in isolation, questions are growing about how many people have jumped on the anti-vaxx train in Spain—where the majority of the population has access to free vaccinations.

As with many vaccine-preventable illnesses, I have never actually seen a case of diphtheria in my career. I certainly remember learning about its characteristic symptoms, including fever, severe sore throat, and a thick “pseudomembrane” that can coat the airway and cause bleeding if one attempts to remove it.

Thanks to a program of immunization against it, it is incredibly rare in the United States. The last reported case was in 2003, in an older (unvaccinated) man who contracted it on a trip to Haiti, and later died.

However, the disease still sickens and kills thousands of people worldwide every year. India may be on the other side of the world, but plenty of people from this country travel to and from that destination, and there were over 2,500 cases there in 2012. The only infectious disease to be wiped off the planet by vaccination is smallpox. Even rubella, which was just declared eliminated in the Western Hemisphere, could still be imported.

Would the doctor in your local emergency department happen to think of diphtheria in a patient with a sore throat and fever? I can’t say I like the odds, which is why an article in a forensic pathology journal advised pathologists that diagnoses in Western countries may only occur at autopsy. That the author needed to tell readers to bone up on the signs because failure to immunize might mean more cases is as ghastly as it is ludicrous.

There is no point in castigating the parents of the boy in Spain. I cannot imagine the guilt and regret they must be feeling right now, and they are themselves recriminating the anti-vaccine advocates whose advice they took to begin with. May their son make a full recovery as swiftly as possible.

But why on earth would any parent voluntarily face the risk of being in the same position? Anyone could reliably have predicted that devastating diseases would start to pop up again in unvaccinated kids, myself included. You can find misguided people willing to pooh-pooh the ill effects of measles, despite its potential for devastating consequences even in healthy children. But nobody who understands diphtheria could wave it away so blithely.

Yet parents who refuse to vaccinate their kids leave them just as pointlessly vulnerable to it, as well. Because diphtheria is part of a combination vaccine, along with tetanus and whooping cough, the same under-vaccinated pockets that contribute to outbreaks of the latter are unprotected against the former, too.

Nobody wants to learn the same devastating lesson as those parents in Barcelona.