The recent outbreak of measles—a highly contagious childhood disease that had been nearly eradicated in the United States—has focused mostly negative attention on parents who choose not to vaccinate their children. Various commentators—such as Jon Stewart in a recent segment on The Daily Show—have also noted that the anti-vaxxers make strange bedfellows. They include liberals who prefer natural, holistic, homeopathic, and other non-traditional approaches to health, as well as libertarian conservatives who object to what they regard as nanny-state meddling in how they raise their children.

But the alliance is less odd than it might at first appear. Viewed through the lens of the constitutional law that will ultimately be implicated should anti-vaxxers take their case to court, the coalition of conservative libertarians and liberal followers of alternative medicine makes sense. Government intrusions into the human body are regarded by both sides as touching on the very core of liberty.

Moreover, today’s libertarian right and liberal left descend from the same broad tradition. Skepticism of orthodox medicine has deep roots in American constitutional culture.

Objections to Government-Mandated Vaccination

To one extent or another, every state requires vaccination of schoolchildren, but nearly all states grant exceptions on religious grounds, and many states also grant exceptions based on other philosophical grounds, such as a parent’s belief that the conventional medical wisdom is wrong or inapplicable to her child in particular. In the current climate, there are calls for limiting or eliminating such exceptions.

Are these calls sensible? Are they constitutional?

Completely eliminating exceptions to mandatory vaccination would clearly be unwarranted for at least one category of cases. Some people have medical conditions that render generally safe vaccines unsafe for them in particular. For example, Carl Krawitt, the father of a young boy with leukemia, made headlines last month when he asked his public school to exclude unvaccinated children: six-year-old Rhett Krawitt’s immune system was too weak to handle vaccines and so he needed to depend on the “herd immunity” of a vaccinated community.

Public vilification of parents who refuse to vaccinate their children has largely spared people like Krawitt. Indeed, the outrage of the pro-vaccination majority appears to be mostly on behalf of people like Krawitt and against those parents who refuse to vaccinate based on other reasons. It thus appears extremely unlikely that any state would require someone like Rhett Krawitt to be vaccinated.

What about other objections? The legal landscape looks somewhat different for religiously-based and non-religiously based philosophical objections to vaccination.

Religious Objections

Neither the federal Constitution nor any federal law would stand as an obstacle to eliminating religion as a basis for refusing to vaccinate children. However, in most states, either the state constitution or a state statute similar to the federal Religious Freedom Restoration Act (RFRA) that was at issue in last year’s Hobby Lobby case provides for religious exceptions to any state or local law that substantially burdens religious exercise.

Of course, state laws granting RFRA-style protection can be amended or repealed, and state constitutions are generally much easier to amend than the federal Constitution. Thus, the state-level RFRA-style protection could be eliminated.

But even if a state retained a RFRA-style regime, parents would likely lose a claim for a religious exemption from a vaccination requirement, because RFRA-style regimes do not provide absolute protection to religious objectors. Instead, the government may override a religious objection to further a “compelling” interest, and public health would surely count, at least where the vaccination safely and effectively protects against a highly contagious and dangerous disease (like measles).

Accordingly, state court decisions involving religious claims to avoid unwanted medical treatment (such as by Jehovah’s Witnesses declining transfusions) generally fit into a simple pattern: adults may make that decision for themselves but not for their children. Because vaccines provide protection not only for the child who is vaccinated but for other children (via herd immunity), states could likely override religious objections to vaccination.

To be sure, states may choose to retain their exemption for religious objectors to vaccines. And so long as the number of parents claiming religious objections is small, the herd immunity would remain largely intact even if a few religious exemptions were granted. But such religious exemptions would be a matter of legislative grace rather than constitutional entitlement.

The Constitutional Right to Bodily Integrity

We will eventually arrive at roughly the same place for the philosophical objections, albeit via a somewhat circuitous route. The leading precedent is the Supreme Court’s 1905 decision in Jacobson v. Massachusetts, upholding a state law mandating smallpox vaccination over an objection that it violated the citizen’s liberty.

Jacobson was decided in an era when the Court was highly solicitous of general claims of liberty: Just three days after handing down Jacobson, the Justices heard argument in Lochner v. New York, in which they would infamously hold that a state law setting maximum hours for bakers was unconstitutional. Yet even in that libertarian era, the Court rejected a challenge to the vaccination law.

One might think that if even the Lochner-era Court was unimpressed by the liberty to avoid vaccination, the modern Court would be even less sympathetic to such claims. But the modern case law is not so clear-cut. Although the Supreme Court overruled Lochner in the late 1930s, subsequent cases make clear that while claims of economic liberty no longer go far, the modern Court affords special solicitude for freedom from physical invasions of the body.

For example, in 1952, in Rochin v. California, the Court invalidated a conviction based on evidence obtained by police who forced an emetic down a suspect’s throat, leading him to vomit up two capsules containing illegal drugs. In a 1985 case, Winston v. Lee, the Court held that the Constitution forbade Virginia authorities from performing surgery on a suspect to recover a bullet that would be used as evidence against him.

As the Supreme Court explained in 1992 in Planned Parenthood v. Casey, Rochin, Winston, and other cases protect a constitutional right to “bodily integrity.” Casey was itself an abortion case. In 1973 the Court in Roe v. Wade had located the abortion right chiefly in a line of precedents regarding individual autonomy with regard to decisions about parenting and contraception, but in Casey the Court cited Rochin and Winston to root the abortion right in bodily autonomy as well: Laws proscribing abortion require a woman to use her body to gestate a fetus.

Perhaps most directly, the Supreme Court’s 1990 opinion in Cruzan v. Director, Missouri Dep’t of Health, assumed that the Constitution protects the common law right of a competent person to refuse medical treatment—even if the refusal would result in death. At common law, unconsented medical treatment would be a battery, an invasion of bodily integrity.

Conservatives Embrace Bodily Integrity Too

The Supreme Court cases finding a constitutional right to bodily integrity swing liberal. They protect criminal suspects, abortion, and (at least in a limited way) a right to die. But conservatives also embrace the right to bodily integrity, especially with respect to medical treatment. The fight over Obamacare shows how.

In arguing that the so-called individual mandate of the Affordable Care Act exceeded the power of Congress, conservatives likened the obligation to purchase health insurance to a mandate to eat healthy foods, especially broccoli. The government and other defenders of the law responded that the health-insurance purchase mandate was not analogous to a broccoli consumption mandate, but it was largely common ground that the government lacks the power to force people to eat broccoli. Why? Because, as I later explained in a law review article, forced broccoli consumption would violate the right to bodily integrity, a right beloved of left and right alike.

Nor is the cross-ideological resistance to medical mandates a recent phenomenon. Historian and American University law professor Lewis Grossman wrote a fascinating article in the 2013 Yale Journal of Health Policy, Law, and Ethics, tracing the roots of what he calls “American health libertarianism” all the way back to the Founding. Interestingly, the father of health libertarianism was also a Founding Father: although physician Benjamin Rush practiced (what was then) orthodox medicine, he advocated freedom of choice for patients. His legacy continued well into the nineteenth century and beyond.

Health libertarianism made good sense at a time when doctors practiced bloodletting to balance the “humors” of the body. But why does it persist in the modern period, when medicine is science-based?

Part of the answer is that much medical practice is not based on science. Doctors adhere to the standard of care provided by other doctors, even if the treatment or medicine they prescribe is ineffective or worse. Thus, various provisions of the Affordable Care Act create incentives for medical professionals to move from their traditional approach to “evidence-based medicine,” in which treatments are systematically evaluated based on outcomes. Until medical practice becomes more pervasively evidence-based, some skepticism towards doctor’s orders will remain justified.

Still, health libertarianism is often itself not evidence-based. For example, the persistent belief that vaccines cause autism, despite the overwhelming evidence that they do not, shows that health libertarianism—on both the right and the left—is not just healthy skepticism. As Grossman explains with respect to earlier periods of American history, so too today, health libertarianism is part of a broader culture of libertarianism, populism, religious freedom, and other values that cut across contemporary left/right divisions. “Liberal” and “libertarian” share more than a common linguistic root.

Overriding Bodily Integrity

Despite the cross-ideological consensus behind the right to bodily integrity, the courts would likely reject a right against vaccination on bodily integrity grounds for roughly the same reason that they would reject such a right on religious grounds. Infringements on the right to bodily integrity must satisfy the same compelling interest test as RFRA-style limits make applicable to infringements on religious liberty. And while a competent adult may have the right to refuse medical treatment despite its adverse impact on him, the state has a compelling interest in protecting others against infectious disease that is sufficient to override the right to bodily integrity.

Anti-vaxxers could argue that vaccines—or particular vaccines—are not safe or effective, and that therefore, mandatory vaccination requirements are not “narrowly tailored” to the government interest in public health. But in recent years, the Supreme Court case law has been particularly hostile to this sort of claim.

Indeed, in upholding the federal Partial Birth Abortion Ban Act in the 2007 case of Gonzales v. Carhart, the Court credited a government-approved medical judgment that was itself highly dubious. Here, by contrast, the weight of medical opinion clearly favors vaccination, so the courts would be especially unlikely to credit an anti-vaxxer claim that the science does not support vaccination.

Despite the fact that the anti-vaxxer case would likely fail in a court of law, do not count it out in the court of public opinion. Although current sentiment runs against the anti-vaxxers, they tap into a deep vein of American liberalism and libertarianism. Even if they lose this battle, they may yet win the war.