For all of the medieval practices that ISIS imposes on the Syrians and Iraqis living under its rule, there is one area where the terrorist group has so far been tolerant: vaccines.

"An unexpected success of the polio immunization campaigns in Syria and Iraq has been the access granted to vaccinators in territory controlled by the militant group calling itself the Islamic State," according to the Integrated Regional Information Networks (IRIN), a humanitarian news service formerly part of the UN.

The UN has called the polio immunization campaign in Syria — which had an outbreak in 2013 — a significant success. While it's possible the disease could come back, 8,500 health workers got as close as they could to immunizing everyone, especially children.

According to workers with the anti-polio campaign, ISIS allowed vaccinators even into areas where they had forbidden other humanitarian. Partly this was presumably in deference to local Syrians and Iraqis who want the vaccine, but also out of simple understanding that polio is bad and vaccines are good.

The head of an NGO that runs the vaccines recounted to IRIN that they reached out to ISIS: "We told them, ‘This polio — it doesn't care about lines. It goes cross-line and cross-border as it wants.'" The Washington Post reported in June that ISIS members had in some cases gotten their own children vaccinated, or had helped facilitate safe passag

On the narrow issue of vaccination, this puts ISIS ahead of some Americans who oppose vaccination for children. American anti-vaccination proponents have focused on the MMR (Measles, Mumps, and Rubella) vaccine, though, rather than polio, after a now-retracted study with false data, published in 1998, suggested a connection to autism. Still, polio has come up; Ron Paul, in making the case that it was okay for some parents to refuse vaccines, said in 2007, "If you didn't take the vaccine for polio, you're not a danger to me. You're a danger to yourself."

As Sarah Kliff put it, writing in response to Chris Christie's characterization of vaccination as a personal choice, "Vaccination is not a personal decision. It has the potential to affect hundreds, maybe thousands, of other people."

ISIS is perhaps the cruelest, most barbaric group on earth today. It does many things that are far worse than denying vaccines to children. But that makes it all the more striking that even ISIS sees the value of immunizing children against contagious diseases.

ISIS's pro-vaccine stance is particularly striking given that other Islamist extremists, such as the Pakistani Taliban, have opposed vaccines, calling thema "conspiracy of Jews and Christians to make Muslims impotent and stunt the growth of Muslims."