The great French essayist Montaigne (1533-1592) wrote about everything. He’s one of the inventors of the essay as a genre, though there are roots as far back as Plutarch and Seneca in the ancient world. Montaigne used the word “essais” to mean something like “informed trial balloons,” and he very frequently ended some passage or assertion or conclusion by saying, “Que sais-je?” (“What do I know?”).

That’s the kind of modesty and skepticism that Jefferson admired. To Edmund Randolph, Jefferson wrote, “I think it is Montaigne who has said that ignorance is the softest pillow on which a man can rest his head. I am sure it is true as to everything political, and shall endeavor to estrange myself to everything of that character.”

So, let me begin and end this little essay on vaccination by saying, Que sais-je?

My mother had a mild case of polio when she was in her late teenage years. At the time, Franklin Delano Roosevelt was the most famous polio victim in the world. My mother suffered no debilitation from her bout of polio so far as we know, though she was a strong, outspoken, opinionated, take-no-prisoners sort of woman, whose nickname for one of my women friends was Dennis Dimwit, a term she routinely used in her presence. So, who knows?

Polio is very nearly eradicated, once and for all, thanks to Enlightenment science and in part to Rotary International, a wholly good organization in spite of the jocular fines, occupational badges, decades of refusing to admit women and the occasional Babbitry. I think it was Mencken who said the first Rotarian was the first person ever to call Jesus “Jack.”

Polio is proving more difficult to eradicate than smallpox, in part because there is, it’s only fair to report, a vaccine-induced strain that science has not yet found a way to prevent. But in the United States, at least, polio is virtually nonexistent, thanks to Jonas Salk’s invention of the vaccine in 1955, the year of my birth, not in time for my mother or in time for one of the two or three greatest presidents in American history.

Smallpox has been one of the greatest scourges of humankind. It’s estimated that the disease killed more than 2 billion people before we finally started to get it under control in the 18th century, first by inoculation and later by true vaccination, pioneered by the British physician Edward Jenner. Smallpox vaccination has been so profoundly effective that 25 years ago, there was actually a debate in epidemiological circles about whether to snuff the very last of it out forever, or to keep a teeny bit of it alive in a tightly sealed and controlled container just in case for some reason we do not now understand we might need to study it down the road. Think of that! A serious debate about whether to exterminate it once and for all or to preserve it because some day in some way it may turn out to be important to our understanding of the nature of contagion.

On the surface, vaccination would seem to be a no-brainer — that no rational being could possibly resist medical breakthroughs that have saved millions, perhaps billions of people from disease, pain, disfiguration, shortened lives and death.

If you told Thomas Jefferson that there were chemical substances that could prevent or cure the diseases that have plagued humankind for millennia, from yellow fever (the 1793 outbreak in Philadelphia killed one in six residents) to measles, from mumps, tuberculosis, chicken pox, whooping cough (which killed his daughter Lucy in 1784), to smallpox, he would rejoice and bow in reverence to the majesty of science. If you told him that a significant minority of Americans chose to refuse to have their children vaccinated (for several different reasons), he would shake his head in sadness, and quote from his letter to Charles Clay in 1790: “The ground of liberty is to be gained by inches, and we must be contented to secure what we can get from time to time and eternally press forward for what is yet to get. It takes time to persuade men to do even what is for their own good.”

A number of infectious diseases are making a comeback thanks to vaccine refusers, among them true plague, mumps, measles, tuberculosis, chicken pox and scarlet fever. I know some of the vaccine detractors. Perhaps you do, too. They are firm, even fierce, in their insistence that vaccines can lead to unintended side effects, including — they allege — autism; that the big pharmaceutical corporations are running a very profitable scam in persuading doctors to force vaccines into our bodies, including flu shots; and that if American liberty means anything, it means that parents have the right to decline having their children vaccinated. If we are not free to raise our children as we wish, what good is liberty? Some parents refuse to have their daughters receive the HPV vaccine, which prevents cervical cancer because they say that it encourages promiscuity and premarital sex. I lived in a rural village in Kansas that refused to give young people access to condoms on the same principle. Five students of the graduating class were pregnant. Apparently, they didn’t just say no.

I have no doubt that the big pharmaceutical companies engage in appalling profiteering and that their first purpose is not the health of the people of the world. I’m sure in some few cases things go wrong with vaccines. I believe in liberty. At this point, I suppose I hope that the number of vaccine refusers remains small so that we can prevent the spread of these dread diseases in spite of their (to my mind, largely irrational and even irresponsible) preference for liberty over public health.

I disagree with what they do, but so far, I defend to the death their right to do it. And it may be to the death, if you think about it.

Just ask the Mandan Indians of my home state North Dakota. Once a proud and mighty earth lodge people living in nine or perhaps even 13 well-zoned municipalities at the mouth of the Heart River at today’s Bismarck, they had a population of perhaps 22,000 at the time of first contact with white Europeans, or other native Americans who had had contact with white Europeans. By the time Lewis and Clark arrived in 1804, they had been reduced by the first of two massive smallpox epidemics from being one of the most puissant tribes of the Upper Missouri to a semi-refugee people who had moved up river to seek protection and more community from their cousins the Hidatsa. When Lewis and Clark arrived, they had a population of approximately 1,250, about 6 percent of their former numbers. In 1837, a trade boat operated by the American Fur Company knowingly but not deliberately brought a new smallpox outbreak to the Mandan. By the time that epidemic had run its course, there were fewer than 140 Mandan left on Earth.

At Jefferson’s instigation, Lewis and Clark actually carried a vial of the smallpox vaccine with them on their journey to the Pacific. Unfortunately, the culture had become inert before they could vaccinate a single Native American. I regard Jefferson as a hero in the history of epidemiology.

OK, let’s assume that a teeny eenie handful of vaccine recipients have significant negative reactions to vaccines. Let’s agree without debate that Big Pharma (as its critics term it) is as greedy and unscrupulous as any other giant capitalist entity. Let’s even honor the spirit of liberty in the refuseniks.

OK, Montaigne. I agree: Que sais-je?

But the simple fact is that a few doubters have the luxury of being openly skeptical about vaccines in the 21st century precisely because we have gotten on top of most of the catastrophic infectious diseases since the scientific revolution of the 17th century and the Enlightenment beginning shortly thereafter. If smallpox were still killing off 80 to 94 percent of our towns and cities every twenty years or so, you can bet that those same people would be crying loudly for scientific and even government intervention.

Just ask the Mandan.