In this photo illustration, vials of measles, mumps and rubella vaccine are displayed on a counter at a Walgreens Pharmacy on January 26, 2015 in Mill Valley, California. (Justin Sullivan/Getty Images)
Opinion writer

The measles outbreak that began at California’s Disneyland — and spread like pixie dust — along with several other, smaller flare-ups, has health officials warning of worse to come. Preventable infectious disease is making its return to the developed world, this time by invitation.

The scientific consensus on measles is effectively unanimous: 1) It is not trivial. Children with measles can get seriously ill, and there is chance of complications such as middle ear infections, pneumonia and encephalitis. 2) Measles is highly transmissible — one of the easiest viruses to get or give. 3) The measles vaccine is highly effective — one of the most successful against any virus or microbe.

I’ll turn “4)” over to Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases: “The ‘evidence’ that measles vaccination is associated with serious adverse events such as autism and other afflictions,” Fauci told me, “has been completely discredited by a number of independent scientific ­bodies.”

Yet, a significant minority of parents — often well-educated parents — are opting out of vaccination. Many states (including California) make it relatively easy to refuse vaccination for “philosophic” reasons. This does not, I suspect, mean that people are reading Immanuel Kant or John Stuart Mill; it means they are consuming dodgy sources on the ­Internet.

Resistance to vaccination on the left often reflects an obsession with purity. Vaccines are placed in the same mental category as genetically modified organisms (GMOs), DDT and gluten. But the problem with organic health care is that the “natural” rate of child mortality is unacceptably high. Organically raised children can get some very nasty ­diseases.

Opposition to vaccination on the right often reflects an obsession with liberty — in this case, freedom from intrusive state mandates. It has always struck me as odd that a parent would defend his or her children with a gun but leave them vulnerable to a microbe. Some conservatives get especially exercised when vaccination has anything to do with sex — as with the human papillomavirus (HPV) vaccine — on the questionable theory that teenagers are more likely to fornicate if they have a medical permission slip (or less likely to without it).

Whether hipsters or home-schoolers, parents who don’t vaccinate are free riders. Their children benefit from herd immunity without assuming the very small risk of adverse reaction to vaccination. It is a game that works — until too many play it.

Herd immunity requires about 90 percent vaccine coverage. Some children with highly vulnerable immune systems — say, those being treated for leukemia — can’t be vaccinated for medical reasons. When the number of non-medical exemptions from vaccination gets large enough, the child with leukemia becomes the most vulnerable to the spread of disease.

The government (in this case, state governments) has the responsibility to keep vaccination rates above 90 percent, which benefits everyone. This requires burdening the freedom of parents in a variety of ways — not putting them in jail if they refuse to vaccinate but instead denying them some public good (such as public education) and subjecting them to stigma (which they generally deserve). As the rate of vaccination goes lower, the level of coercion must increase — making exemptions more difficult and burdensome to secure (as California needs to do).

This issue is important in itself. It also demonstrates a point that is properly called “philosophic.” Vaccination is communitarianism in its purest, laboratory form. The choices of citizens are restricted for a clearly (even mathematically) defined social good.

Things get murkier with other kinds of goods. Does the same coercive power apply to chronic diseases involving lifestyle choices? Government has taken a position against the use of tobacco. What about substances such as sugar, salt and saturated fat?

Does the common good extend to the moral and social health of a community? Maybe just to the moral health of people younger than 21 or 18, who can’t buy or consume certain things? How about prostitution, which degrades women and men (even as willing participants) and results in a squalid social atmosphere? How about the legal availability of concentrated forms of tetrahydrocannabinol (THC), the active ingredient in marijuana?

In all these matters, there is a balance between individual rights and the common good. This may sound commonplace. But some Americans seem to believe that the mere assertion of a right is sufficient to end a public argument. It is not, when the exercise of that right has unacceptable public consequences, or when the sum of likely choices is dangerous to a community. Sometimes we need 90 percent of the public to make the right choice, or innocent people suffer.

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