Saturday, March 22, 2008

Epidemiological free riders

The New York Times has an infuriating story about a recent outbreak of measles in San Diego, centered around a group of families who refused to get vaccinated against the disease. In all, a dozen kids got sick.

Now, if all dozen of these kids were from the families that had refused the vaccine, one wouldn't have much cause for a beef. These parents are recklessly endangering their own children based on a misinformed sense of the dangers associated with vaccines. But it's a free country, after ll, and people have a right within limits to endanger their own children. (A hard-hearted person might describe this as permitting Darwinian principles to do their work.)

But the thing is, it's not just their own children these jerks are endangering. A quarter of all those who got sick were children too young to receive the vaccine. I think the families of the sick babies should seriously consider lawsuits against the families of those who refused the vaccines and thus knowingly endangered their fellow citizens. The key word here is "knowingly" -- these people know that they are endangering others through their inaction--the very definition of negligence. The story quotes one parent of an unvaccinated child as saying, "I refuse to sacrifice my children for the greater good."

Legal animus aside, the real story here is about what is best described as "epidemiological free-riding," and how to prevent it. For most diseases, the percent of the general population that needs to be vaccinated in order to prevent epidemic outbreaks is around 80%. That is, if that percentage is reached, then the virus or bacteria cannot find enough unimmunized hosts to break out into a large, self-sustaining chain of infections.

This of course is what creates the opportunity for free-riding. Since you don't actually need to vaccinate the whole population in order to prevent epidemics, people have an incentive to avoid the immunization themselves and get the rest of the population to take the shots. As long as that 80% target is hit, the remaining 20% can avoid the pain and potential (though usually tiny) risks associated with getting the vaccine, while still accruing all the epidemiological benefits of having the mass of the population vaccinated. Of course, if everyone (or even just a quarter of the population) takes this selfish view, then the epidemiological benefits evaporate. The right way to look at this situation is that those who refuse vaccinates are the epidemiological equivalent of people who dodge taxes but still use public services like streets, or people who pirate software, expecting paying users, in essence, to sponsor them. Except epidemiological free riding is much more pernicious: tax dodgers and software pirates merely impose some additional financial costs on their fellow citizens, whereas these vaccine dodgers endanger the actual physical well-being of their fellow citizens.

There are two ways to deal with this problem. One way is to mandate vaccines. That's the way it's done in virtually all developed countries. In the United States, though, such requirements are often considered intolerable violations of personal liberty. The other way--one that respects personal liberty more, but also demands more personal responsibility--is to hold the unimmunized liable for the damage they inflict on their fellow citizens through their negligence. Of course, that at minimum involves civil lawsuits, which in turn means bringing those dreaded "trial lawyers" into the equation. (This underscores the way that trial lawyers are in fact an necessary safety feature in a society dedicated to personal liberty--something that the anti-trial lawyer political faction never quite manage to recognize. But that's a topic for a different blog post.)

As I see it, I think mandating vaccinations is perfectly reasonable even with a very narrow (that is, classically liberal) understanding of the proper scope of the state. As Thomas Jefferson famously remarked, "The legitimate powers of government extend to such acts as are injurious to others," that is, such acts by others as either "pick my pocket or break my leg." Well, this is a classic instance where the acts (or non-acts) of others have the potential to "break my leg," and that therefore should certainly be seen as a reasonable domain of state legislation. And if the state refuses to do its duty, then it's up to the trial lawyers to put things right.

1 comment:

zachawry said...

Schools should randomly dose children with polio, measles, mumps, and other pathogens. Maybe only a few per class.

Those who are immunized will be fine, and parents of those who are not will be sufficiently motivated to make sure they are.