A measles, mumps and rubella vaccine. (Eric Risberg/AP)

Another massive study has discovered no causal connection between the MMR (measles, mumps, rubella) vaccine and autism.

This time, the study’s cohort consisted of every child born in Denmark from 1999 through December 2010 — more than 650,000 children. The conclusion? “The study strongly supports that MMR vaccination does not increase the risk for autism, does not trigger autism in susceptible children, and is not associated with clustering of autism cases after vaccination.”

So the arriving children of an entire country stand witness against a destructive but durable myth. Yet the question remains: Can you kill a myth with a study?

Measles is the purest of test cases. “It is one of the most contagious viruses known to man,” Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, told me. “The measles vaccine is one of the most effective vaccines known to man — 97 percent effective. And, historically, measles is one of the great killers of children. Yet, there is a reluctance on the part of some parents to give the vaccine to their children. This just makes no sense, if you just think about it for a second.”

But there is the rub — assuming a second of thought. For some on the left and right, the general revolt against authority has become a revolt against the medical profession. This may be motivated by suspicion of pharmaceutical companies and the business of medicine. Or by a resentment against governmental compulsion. In a recent hearing on vaccines, Sen. Rand Paul (R-Ky.) admitted the medical value of vaccines but added, “I still do not favor giving up on liberty for a false sense of security.”

What Paul — a part-time ophthalmologist but full-time libertarian crank — calls “a false sense of security” is technically known as herd immunity. This is the level of vaccine coverage at which transmission of a pathogen becomes very difficult in an entire population of people. Achieving that level — 93 to 95 percent for measles — not only protects the health of a community, but it also protects those who really can’t be vaccinated for medical reasons such as immune system problems or infants less than a year old.

Paul is engaged in a particular type of fallacy. He is applying standards of political philosophy to a scientific field. Opponents of vaccination claim what they call “medical freedom.” But that is like asserting religious liberty in the realm of chemistry. These fields employ different categories of knowledge. The scientific method is oriented toward an objectively discernible reality in a way that political philosophy is not. There is no lab test proving John Locke’s politics superior to Karl Marx’s politics.

But this was exactly what Marx claimed in developing his “scientific socialism.” He imagined that history moves in a scientifically evident pattern, which would leave no room for minority rights. Those who employed Marxism most rigorously saw resistance to oppression as hopeless opposition to a law of nature.

Paul is making a category error in the other direction. Epidemiology is a scientific discipline. And public health is the application of this discipline to a community of human beings. It really doesn’t matter what John Stuart Mill or Ayn Rand had to say about herd immunity. Given the nature of the measles virus, 93 to 95 percent of a human population needs to be covered for a community to be protected. If purely voluntary methods produce that level of coverage, that is fine. If the needed level can only be achieved by requiring vaccinations for all public school children, that is also fine. If the zombie apocalypse comes, even more stringent health measures might be justified.

The protection of human life is ultimately a moral commitment. But the methods to ensure public health are well established, and should be calibrated to achieve a scientifically definable public good. Those methods, like good surgery, should be minimally invasive. But the goal is not up for democratic grabs, and has no partisan definition.

Politics does make a huge difference to public health in one way. When politicians give legitimacy to dangerous and disproven scientific theories — as both Paul and President Trump have done on vaccinations — they are encouraging a lower level of coverage, which makes a higher level of compulsion necessary. So it is the vaccination skeptics who are making intrusive public health methods more likely. That just makes sense, when you just think about it for a second.

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