Florence, Italy — It was here in 1614 that Tommaso Caccini preached a sermon in the church of Santa Maria Novella denouncing Galileo and other scientists who held the heretical view that the Earth circles the sun. This was one of the main triggers that brought Galileo to the attention of the Inquisition.

There are many monuments to Galileo in Florence. None, at least that I’ve seen, to the Dominican friar who persecuted him. But in Italian politics, the spirit of Caccini — the sacrifice of scientific reasoning to ideology — remains at work.

Italy’s right-wing coalition government — composed of conservatives and internet-based populists (including former communists) — has provided a political home for the anti-vaccination movement. The hard core of that movement, according to public health surveys, is quite small. But its arguments reinforce the questions and fears of a broader 15 to 20 percent of the Italian population who are seriously hesitant about vaccination.

A 2017 Italian law expanding the number of mandatory vaccinations from four to 10 produced significantly greater coverage, as well as a populist backlash. Italy’s new interior minister has said that the requirements are “useless and in many cases dangerous.” One senator from the government coalition has compared vaccination scars to “branding for beasts.” The new health minister recently sacked the government’s entire, 30-member science advisory panel, presumably to get advice more amenable to populist ideology.

The arguments of the Italian anti-vax movement are the same as elsewhere. They believe that vaccinations are somehow associated with autism, tumors or allergies. Since there is no reputable science to support this view — none at all — they turn to the language of parental choice and “more freedom” for families in health care. And they often add a conspiratorial element, accusing Big Pharma of making profits off unnecessary vaccinations.

The problem, of course, is that when too many parents in a community choose to believe these myths, herd immunity is lost. (For a highly infectious disease like measles — which can be contracted through a cough at an airport — a vaccination rate of 95 percent is necessary to effectively prevent its spread.) And when herd immunity is lost, this leaves children who truly can’t be vaccinated — children with weak immune systems, cancer and chronic illness — vulnerable to dangerous infections.

With the assumption of power, Italy’s governing coalition has become less direct in its attacks on vaccination. But it has chosen this moment — during an outbreak of measles in Italy that has led to thousands of infections and at least ten deaths — to reassess if vaccinations should be mandatory. One prominent and soft-spoken Italian medical researcher I met in Florence, Lorenzo Moretta, became less soft-spoken on this subject. “It is not ideology,” he said, “it is idiocy.”

Some of the resistance to vaccination is natural. The idea of giving healthy people a medical treatment that involves risks has always raised questions. And the dramatic success of vaccinations has (paradoxically) made the risk of infectious disease seem more distant and less urgent.

But some elements in Italy and the U.S. have fed these sentiments for ideological reasons. The populist revolt against the “establishment” has been extended from the governing establishment to the medical and scientific establishment. It involves the questioning not only of various authorities but also of the idea of authority itself.

Giovanni Rezza — the head of Italy’s version of the National Institutes of Health — described to me “a loss of the sense of authority — a mistrust of all sectors of society.” He remains confident that most people can be reached by medical professionals carrying sound information about vaccination. But this is complicated, he admits, when “authorities seem corrupted.”

There is more at work here than institutional distrust. The problem reaches the realm of epistemology. Radical populists create their own elaborate universe of ideological loyalty and debunked science, of a type that would have been familiar to Caccini. They inhabit a clean, comfortable world of their own creation, denying any unfavorable news as “fake news” and any unfavorable science as biased and corrupt. A revolt against the establishment becomes a revolt against the scientific method, which becomes a revolt against reason itself.

But pathogens really don’t care about political constructs. They lurk in small pockets of humanity, and return with a vengeance when humans are not vigilant. When politics lessens that vigilance, it can leave not only confusion, but victims.

— Michael Gerson is a columnist for Washington Post Writers Group.