Anti-vaxxers can ignore the needle but not the damage done.

Photographer: Justin Sullivan/Getty Images

Your Right to Skip Shots Ends Where My Kid Begins

Megan McArdle is a Bloomberg View columnist. She wrote for the Daily Beast, Newsweek, the Atlantic and the Economist and founded the blog Asymmetrical Information. She is the author of "“The Up Side of Down: Why Failing Well Is the Key to Success.”
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Like many people on the Internet these days, I feel pretty strongly about vaccination: I'm for it. So how to convince anti-vaccine parents that vaccination is in the best interests of their child and society?

In the past, I have had some pretty sharp words about parents who do not vaccinate their children. At the time, people chided me: I might be right, but scorn wasn't going to persuade anyone. 

Perhaps they're right. To be sure, scorn (and stiff legal sanctions) has curtailed a number of once-common behaviors, such as drunken driving. But for scorn to work, anti-vaccinators have to want the good opinion of the people who scorn them, and they don't; they cluster in communities where their behavior is affirmed. In a situation like that, scorn doesn't convince, but instead solidifies their identity with the community that welcomes them.

Vilifying Vaccines

But what does work? Not telling people about the horrors of the diseases they are helping to spread. Nor does explaining the science calmly and patiently seem to do much good. The autism-vaccine connection has been about as thoroughly discredited as possible -- the paper retracted, the author thoroughly discredited. It still persists, even though logic suggests it never should have started: After all, if the measles vaccine gives you autism, then why wouldn't actual measles? So do complaints about thimerosal and mercury, even though thimerosal was removed from vaccines more than a decade ago, with no obvious impact on the rate of autism diagnoses.

Maybe the answer is "nothing works, because their behavior is both totally antisocial and completely rational."

First, a short primer on why vaccines work at all. Basically, they train your child's immune system to look for certain infectious agents, bacteria or viruses that can make you sick, by giving them a small amount of a weakened strain that has little power to make them sick but is close enough to the real thing that when the immune system sees it again, the killer cells will spring into action and say "Destroy! Destroy! Destroy!" 

OK, you knew that. But what a lot of people don't seem to understand too well is the limits of vaccination. Over time, your immunity can wane. Or you can get HIV, or medical treatment that suppresses your immune system, such as chemotherapy, or the immunosuppressive drugs used to treat autoimmune diseases or keep your body from rejecting an organ transplant. Now you're at risk for catching the disease.

That's why we rely on something called herd immunity. Basically, if you vaccinate most people, the odds of the disease meeting a receptive host fall, and the disease dies out even though not every single person has been vaccinated or retains their immunity. If 99 percent of the population has been vaccinated, then a single person with measles is unlikely to infect anyone else before they get well (or die). On the other hand, if, say, only 90 percent of the population is immune, then the odds of finding a new victim increase dramatically. The level of herd immunity required to eradicate a disease varies depending on how infectious it is, but for measles it's about 92 percent. As herd immunity wanes, society develops reservoirs of contagion from which epidemics like the current one can spread.

Children are a great reservoir of disease. Their immune systems are still developing. Their devotion to personal hygiene is minimal. Those of school or day-care age spend all day in the company of other children, touching each other and everything else, failing to wash their hands or blow their noses into a clean tissue, and putting unlikely things into their mouths. That's why we call these things "childhood diseases" -- not because only children can get them, but because once school was invented, children tended to get them, spread them to everyone else and then become immune. In the process, some of them ended up paralyzed, or blinded, or otherwise disabled, or dead.

Vaccination denied the disease its reservoir. It carried a very small risk -- some children are allergic to the vaccines or have other rare, adverse side effects. But the risks were tiny compared to the numbers of children and adults who used to suffer or die from the complications of getting the actual diseases. Universal vaccination of children didn't just save a lot of precious kids from a lifetime of suffering or the grave -- it also meant that adults didn't have to worry about whether their immunity had waned as they aged.

The magic of herd immunity makes it (almost) completely safe for some number of parents to stop vaccinating their children. If everyone else is vaccinating, the cost-benefit analysis is clear: You can avoid a crying child, and the tiny risk of adverse side effects, at basically no risk to your kid. Why should you spend a lot of time listening to some pedant lecture you about herd immunity? From your individual perspective, the cost of being wrong and not vaccinating is zero; your kid probably won't get sick anyway. Whereas if you're right, the potential cost of being right, and vaccinating anyway, is huge: Your kid could end up dead or autistic.

Unfortunately, there's no way to assure that we will get to that number and stop -- and we haven't. Enough parents have refused vaccination that the disease has new reservoirs. As with other epidemics we've seen, many of the people who got sick in the most recent outbreak had in fact been vaccinated, but they lost immunity over time. Anti-vaxxers took this as evidence that vaccines don't work, but that's wrong. Vaccines work -- but only if enough people use them. What anti-vaccination parents are doing really is incredibly dangerous -- just ask a long-ago commenter in one of my threads who caught measles at the age of 15 months from an unvaccinated child and ended up with scarred corneas for the rest of their life. But it's only dangerous if a lot of people do it at once.

Unfortunately, this is an incredibly difficult message to get across. Human beings are not natural statisticians; our brains prefer simple cause and effect.

And there is a certain logic to the cost-benefit analysis the anti-vaccine parents are doing. Why put your child at the risk of even a tiny danger in order to make a tiny contribution to a vast public good? Collective-action problems are one of the hardest nuts to crack in social science, or society, and for good reason. They are especially hard to crack when you are talking about parents and their children. One need only look at the number of parents, including many leading Democratic politicians, who have opposed school choice on the grounds that it would ruin public schools by "skimming the cream" ... while safely removing their own offspring to tony private schools or equally tony suburbs where the public education systems are basically prep schools that come bundled with granite countertops. When asked about this, they all give essentially the same response: Sure, I'm against cream-skimming in theory, but my kid only has one shot, and you can't expect me to blow it in the name of equality.

There's a distressing possibility that we may just end up stuck with a certain level of disease. If a lot of people get sick, parents will worry more about the disease than the vaccine, and rates will go up; if no one's getting measles, people will worry more about the dangers of the vaccine, and they'll go back down again, until more people start getting measles again. Economist Steve Postrel, husband of Bloomberg View's own Virginia Postrel, likens it to a long-standing problem in finance:

The structure of this problem is similar to the problem of fundamental research in financial markets. If everybody does it, it makes the market efficient, but in an efficient market you're better off indexing and not paying for fundamental research. Grossman and Stiglitz developed a theoretical model wherein the equilibrium outcome had the market just a little bit inefficient while fundamental research just broke even on the margin. Maybe we have an equilibrium level of infectious disease unless vaccines are mandatory.

This seems all too plausible -- and tragic. On the other hand, we have at least a partial solution for free-rider problems: government intervention. This is the purest case for public health laws: preventing people from putting others at risk. And now is the best time to do it, when the number of parents refusing vaccines is still relatively small, and therefore relatively politically powerless. Maybe it's time to stop arguing.

I'm not saying that we should force parents to vaccinate their kids at gunpoint. On the other hand, we might treat vaccines the way we treat drunken driving or car insurance. You have the perfect right to drive your uninsured automobile -- on your own property. I doubt the cops are going to come after you for a DUI on your own back 40, either. But when you enter into public space, you have an obligation to protect others from the possible consequences of your actions: You can't drive recklessly, you can't drive without liability insurance, and you cannot drink a fifth of scotch and then get behind the wheel of a car.

So say to parents: You have a perfect right not to vaccinate your children, and we will not force you. But unless you have a vaccination certificate, a letter from a doctor explaining that your child falls into a small number of well-recognized medical exemptions, or a testament from your minister that vaccinating violates the tenets of a church of which you are an active member, failing to vaccinate your child also means failing to qualify for any public benefits for those children. No tax deduction. No public school, college or municipal activities. No team sports that practice on public land. No federally subsidized student loans. No airplane rides for anyone under 18 unless the TSA gets an up-to-date vaccination certificate. If you will not help society protect itself, then society will deny its help to you, and it will do its best to keep your child out of crowded spaces where they might infect someone.

Is this coercive? Of course. So is putting some stranger -- often an infant, by the way -- at risk of disease and death. Some level of coercion is necessary to protect public health. It is coercive to force you to pay for an expensive sewer hookup rather than dump your waste into the nearest cistern or river. It is also unfortunately necessary to keep cities from becoming death traps. We should try to minimize the coercion as much as possible, which I think this does: If you want to home-school and keep to yourselves, you are free to risk the lives of your own children. But you're much less free to put others at risk.

That wouldn't solve all of the problem; some parents are rich enough not to care. But it would be a start -- and a start is what we need to make, right now. We didn't stomp out drunken driving overnight, either. But we did save a lot of lives.

This column does not necessarily reflect the opinion of Bloomberg View's editorial board or Bloomberg LP, its owners and investors.

To contact the author on this story:
Megan McArdle at mmcardle3@bloomberg.net

To contact the editor on this story:
Brooke Sample at bsample1@bloomberg.net