Saturday, January 31, 2015

Distributing the herd

Because of the spreading Disneyland measles cases, there’s been a lot more national conversation about vaccination, exemptions, and herd immunity.

Vaccinations aren’t 100% effective, and populations aren’t 100% vaccinated. Herd immunity protects the unvaccinated as long as the vaccination rate is high enough overall, because there aren’t enough new people for a sick person to infect for the disease to keep spreading. However, our herd immunity to measles is visibly facing two challenges: declining vaccination rates and clustering of unvaccinated populations. An insufficient herd immunity means that parents who choose not to vaccinate their children are endangering lots of other people in addition to their own children.

We have to allow medical exemptions to vaccination, because of allergies and certain medical conditions that would make the vaccine unsafe for those people. A tiny fraction of people claim a religious objection, but an increasing number of people are claiming a nebulous “personal beliefs” exemption. And because those personal beliefs are spread through personal conversations between parents and local peer pressure, there are clusters of people refusing vaccination for their children.

Requiring that parents consult a (hopefully sane) pediatrician and get the pediatrician’s approval before being allowed to opt out of vaccination is a reasonable step, but it doesn’t go quite far enough. There are pediatricians who are willing to go along with skipping vaccinations, as well as many who are not. We need to limit how many exemptions an individual pediatrician can hand out, and setting that limit to the percentage that would preserve our herd immunity is the only safe approach. If we need 97% of people to be vaccinated against measles in order to preserve our herd immunity, and a pediatrician has 1000 patients, the pediatrician should only be allowed to have a maximum of 30 patients who skip the measles vaccination. If you’re the 31st patient and you really want to skip the measles vaccination, you’ll need to find a different pediatrician.

This approach makes it more difficult for parents who want to skip vaccinations for their children, at least until this anti-vaccine nonsense dies down. Good. It should be difficult to endanger other people. This approach prevents pediatricians who don’t have the courage to stand up for their medical training and their other patients from causing too much damage by handing out obscene numbers of exemptions. More importantly, it forces some distribution of the unvaccinated. And forcing the unvaccinated to step away from each other is an important step to take.

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