A couple of weeks ago I wrote a post about the difficulty many people have grasping the logic of collective action problems — where the outcome of an interaction is bad, but where no individual has an incentive to stop doing the thing that is leading to that bad outcome (here).
I’m reminded of this problem every morning these days, since vaccination has been in the news, first with the NHL players, and now with a measles outbreak in Toronto. The debate over vaccination is a perpetual source of frustration for me, because people insist on treating parents who refrain from vaccinating their children as irrational, whereas in most cases they are not being irrational, they are actually free riding, which is perfectly rational, in at least one sense of the term (i.e. the one used by economists). Thus they should be criticized for acting immorally, as opposed to irrationally. Unfortunately, because that’s difficult to explain, most of the people that I hear making the case for vaccination, especially doctors, present the case far too simplistically. They will claim, for instance, that vaccinations are perfectly safe. This is not true, some vaccinations do in fact carry with them a very small risk of (in some cases serious) side effects. Now the magnitude of that risk is very small, and is therefore easily outweighed by the dangers associated with catching the disease that it protects against. But this is where herd immunity comes in. If everyone else is vaccinating their kid, then your chances of getting the disease are minimal. So why run the risk of the side effects of the vaccination? Let other parents run that risk with their kids. Then you can get the benefits of herd immunity, and avoid the risk of side effects for your child. A classic free rider strategy.
The best way to illustrate this is with a style of diagram that Thomas Schelling used in Micromotives and Macrobehavior (and remains, for me, the clearest way of thinking about it). Graph the benefits on the Y axis, the percentage of the population that is vaccinated on the X axis, then draw two lines showing the level of benefit associated with each strategy — red for the benefits of choosing vaccination, green for the benefits of choosing no-vaccination:
One can see here that when no one is getting vaccinated, there is an obvious benefit to getting vaccinated (and so the red line is well above the green one). (Hence the fact that, several decades ago, when childhood deaths from contagious diseases were an everyday occurrence — or when everyone knew someone in the older generation who had family member die of polio — vaccination was a no-brainer.) Getting vaccinated, however, generates a positive externality. Not only are you less likely to get sick, you are less likely to give the disease to others. Thus as the percentage of the population that is vaccinated increases, everyone enjoys the benefits, but those who are not vaccinated derive a much greater benefit (since they are far more vulnerable to the disease). Meanwhile, those who are vaccinated derive a very small benefit (since they are very unlikely to get the disease in the first place), but they are also running a small risk of side-effects. As a result, as more people get vaccinated, there reaches a point at which the benefits of not being vaccinated actually surpass the advantages of getting vaccinated. As a result, the equilibrium in the population is that x percent will get vaccinated (where x < 100% — resulting in a benefit level lower than the higher level obtainable at 100% vaccination).
Now that having been said, I don’t think a lot of the people who refrain from having their kids vaccinated are consciously free-riding. They are just acting in the interests of their child, construed very narrowly. The phenomenon of herd immunity only impinges on their consciousness to the extent that children getting seriously ill from these contagious diseases is not really something they have any experience of (“when’s the last time you heard of anyone getting small pox?”), and so they start to entertain irrational beliefs (e.g. the vaccinations are just being pushed by “big pharma” trying to make more money) — and they don’t really get penalized for having irrational beliefs, because herd immunity protects them from the consequences. (So while I think there is irrationality, I think the irrationality is downstream from the free rider incentive, in the sense that they are just believing what it is in their interest to believe. In the same way, many people who “don’t believe in global warming” actually just don’t want to change their lifestyle, and are merely adjusting their beliefs to avoid having to acknowledging that they are acting in an anti-social way.)
This all becomes important when it comes to developing a communications strategy for dealing with people who do not vaccinate their children. I’ve heard anti-vaccine parents saying that, before they vaccinate their child, they want assurances that the vaccine is “completely safe.” This is an assurance that they are never going to get. The MMR vaccine, for instance, does produce side effects in some children, some of which can be serious. So the answer is not to say — as I have heard some doctors say — that the vaccine is completely safe. Nor is it to say something that sounds complicated, like “well, there are some side effects, but these are very rare, etc.” (To which twitchy parents respond “RARE? HOW RARE?”) The answer is to say “you are morally obliged to vaccinate your child, regardless of the risk. We are all called upon to make a small sacrifice for the common good. Besides, how would you feel if someone else’s child died, because she caught a disease from your child, because you weren’t willing to run the small risk associated with getting him vaccinated?” In other words, the argument needs to be a moral one, not a prudential one. If only 30% of population was vaccinated (or 42%, as it turns out the rate is at a local Toronto “alternative” school), then the prudential argument works just fine. But once you’re past point x on my little graph (e.g. say 90% vaccination), then the prudential argument doesn’t work any more, and we need to shift to the moral one.
Finally, just a little story. Anyone who looks up the records on my children will see that I made a “conscientious objection” claim for my daughter. I can explain. She got her MMR booster three days before her birthday. Years later we got an official letter from the government saying that our child had not received the required shots at age 6 (or whatever, I can’t remember exactly what age), and so we had a week or so to get it done or she would be kicked out of school. Called to complain and spoke to an almost comically inflexible bureaucrat, who absolutely would not accept that getting a shot at age 5 years + 362 days was, for all intents and purposes, equivalent to getting one at age 6. She was completely committed to making us go out and get it done again. So we chose the course of least resistance, which was to file for an conscientious exemption. I had this awesome plan to write a letter, explaining that we subscribe to an unusual religion called “science,” and that according to our belief system, receiving a vaccine on a Monday is just as effective, overall, as receiving it later in the week, say on Thursday. We consulted with religious officials — known as “doctors” — and they confirmed our interpretation of the holy texts, etc. Sadly, the form didn’t require any sort of explanation or justification, you just had to state that you had some reason for not wanting your kid vaccinated and they took your word for it.