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One morning in 1934, panicked passengers jumped from the deck of the SS Morro Castle as it sank just off the coast of New Jersey. The ocean liner had caught fire, and the passengers had rushed to grab personal flotation devices. But some improperly wrapped the life preservers around their necks. As they fell and hit the water, the torque snapped their spines.

Personal flotation devices save exponentially more lives than they cost. Of the catastrophic boating accidents that occur daily, 84 percent of people who drown were not wearing one. But etch the details of this horrific wreck scene into one’s mind, and a person might become a life-preserver skeptic. Our basic tendency toward short-term thinking means we judge risk based on whatever is in front of us. We draw anxiety disproportionately from wherever we happen to be focusing our attention.

The same psychology applies throughout public health. At the moment, much attention in the U.S. is being paid to vaccines—rather than the diseases they prevent. This week, the actor Jessica Biel drew fiery eyes for lobbying legislators in California to kill a bill that would standardize the process of exempting children from required vaccinations. Biel, perhaps best known for her leading role in 2006’s The Illusionist, expressed concern for the well-being of a friend’s child. She has responded to accusations of being “anti-vax” by contending in an Instagram post that she “believes in vaccinations,” but wants to protect personal freedom: “I believe in giving doctors and the families they treat the ability to decide what’s best for their patients.”

Like life preservers and everything else, vaccines do come with some fleeting risk of unintended adverse outcomes: mostly rashes or fevers, and in extremely rare cases, seizures. But these risks pale in comparison with those of the diseases vaccines prevent. Before the advent of vaccination, measles alone killed some 6,000 children in the United States every year.

This year has already seen more measles cases than any other since the disease was declared eliminated two decades ago. The trend stems from low rates of vaccination, which are making exemptions from vaccine requirements a flash point. California has triggered a reckoning with why exemptions exist at all—and why belief came to factor so heavily into a question of science. When is a health issue a matter of belief, and when is it simply wrong? When is it so wrong that it’s neglect?

No federal law requires vaccination. But every state mandates that in order to send a child to public school—to have that child sit in close quarters with other children all day, every day—parents must take preventive measures to ensure the child does not carry certain dangerous infections. Requirements are implicit in the legal precedent that withholding vaccination constitutes “medical neglect” of a child. Legally, for example, it’s considered neglect to let a cut on a child’s arm get infected and then refuse antibiotics. If that infection had been airborne, as with measles, declining treatment as a child gasps for air would also be textbook neglect. It has been deemed neglect in cases where infectious diseases could have been easily prevented, but weren’t.

Researchers at Ohio State recently reviewed cases across the country from 1905 to 2016 and found that a majority of the time, refusing vaccination was found to be neglect. There was a curious caveat, though. In states with “religious exemptions,” parents did not have to follow public-health mandates to vaccinate their children against measles and other diseases if the parents cited “genuine and sincere religious beliefs.” The Ohio State researchers found that in these states, vaccine refusal did not constitute neglect—or it was considered neglect only if someone’s belief was deemed insufficiently “sincere.”

Religious exemptions have slowly expanded in the United States, to the point that now, in almost every state, parents can opt out of school requirements—and leave a child open to catching and spreading lethal diseases to other children—if doing so is guided by what the state considers a sincere belief. In such cases, the same behavior is not neglect.

Exemptions have expanded to include “personal or philosophical belief” exemptions as well, which are currently offered in 17 states. When the standard is sincerity of belief, the thinking goes, it shouldn’t have to be drawn from a major religion (or even a minor one).

Accordingly, the number of people taking up belief-based exemptions has been steadily increasing, and rates of vaccination declining. The constitutionality of vaccine requirements is well established, and courts have found states are not obligated to grant religious exemptions. Nevertheless, the overall effect of such respect for the concept of personal belief has been that, gradually, vaccine requirements have become requirements in name only.

The return of measles, though, is forcing a breaking point. In 2015, a measles outbreak was traced back to a single child at Disneyland. California health officials saw that the outbreak happened not simply because of one unvaccinated child, but because only 90 percent of kindergartners in the state were fully immunized. To establish herd immunity for measles, a community needs 94 percent of people on board.

This led the state to pass a law that eliminated personal-belief exemptions, making California the first state in recent history to do so, and only the third state in total. (Mississippi did so 35 years ago, and West Virginia never had such exemptions.) The crackdown seemed to work. By last year, kindergarten vaccination rates for the 10 required diseases were up to 95 percent.

California is serving as a model of what could play out across the country—and a microcosm of other debates about science and belief. Several states now have bills in place to repeal nonmedical exemptions. Last month, Maine repealed the personal-belief loophole and is considering a ban on religious exemptions, as is Connecticut. In New York, after hundreds of people contracted measles, Democratic lawmakers proposed a bill in May to make their state the fourth to ban religious exemptions. Republican Representative Anne Dauphinais told the Associated Press in response that the religious exemption “is one thing you just don’t mess with.” But the move polled at an overwhelming 84 percent support, across religious lines. The bill passed on Thursday.

Such moves stand to create a novel problem, though, and a test for the medical profession. There is still one way to get an exemption from required vaccinations: from a doctor. Indeed, there are some immune disorders and other rare scenarios where a child is not medically able to receive a vaccination, and so has no choice but to rely on herd immunity to be protected. But in the past two years, California has recently seen such medical exemptions triple. This has been accompanied by some doctors being identified as purveyors of exemptions, sometimes specifically marketing the service.

Public-health officials have taken this to mean there is need for standardization of the process. The new bill, which Biel is protesting, would help the state identify practitioners who were writing dubious exemptions by having schools notify state health officials in suspicious cases. Patterns of invalid exemptions could be traced to certain providers, who could be penalized or educated as necessary to keep the state’s herd immunity strong.

Overseeing standards of practice for doctors is not a novel concept. In light of the opioid epidemic and overuse of antibiotics, many health advocates believe oversight should happen more readily—if only to identify serious outliers. This could at least help ensure that no doctor is running an exemption mill, a phenomenon that does tend to happen whenever doctors in a private health-care system become the sole gatekeepers for various allowances or services. This has been an issue in cases such as the psychiatric diagnoses that grant kids extra time on standardized tests, or the prescriptions that allow people legal access to marijuana or opioids. (In 2012, I got a medical-marijuana card on Venice Beach by paying $100 in cash to spend five minutes with a doctor. On the wall was a poster with a list of things I could say were bothering me that would warrant marijuana access. This was clearly not the spirit of the law.)

Biel’s lobbying is against this sort of oversight, which would prevent similar suspicious practices by doctors. The actor is stepping in to influence policy that could worsen outbreaks like measles because, as she has publicly stated, it is what she believes. (Biel did not immediately respond to request for further comment.)

In communal undertakings like eradicating infectious disease, the role of personal belief is limited—but not zero. It is exercised through a democratic process where elected officials (and their appointees) implement policies that keep communities safe and well. If public-health officials steer communities wrong, people rally and vote accordingly. The system falls apart, though, when individuals simply declare themselves exempt.

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