Let’s say that you’re a doctor some day. Or a professor, for that matter. And someone (e.g. your patient, a party guest, or friend on facebook) starts talking about the Dangers of Immunization. You could respond with “The anti-vaccination people are misled, crazy or amoral…” but that will be highly counterproductive. I think I’ve got a better one. I must preface, however: this argument applies to life-threatening childhood endemic diseases like polio, not so much to optional flu shots and such, whose risks and efficacy are less well known.

Why a person might not want a vaccine: All medical treatments carry a certain measure of risk. Like crossing the street or taking a bus, everything is a risk at some level. The problem is causation. If you get hit by a bus, it’s not your fault. If you choose to get vaccinated and there are some side effects, then you feel like you’ve screwed yourself. And that is a terrible feeling.
But, look, we need to evaluate risk in a sane and rational way. Let’s say that the choice is between:
1. Doing nothing and taking a 1 in 100 risk of contracting a life-threatening disease

or

2. Take a concrete action which carries a complication risk of 1:1000.

Clearly, your odds are better with option 2. But a 1:100 chance of being screwed by external random events may feel preferable to a 1:1000 chance of screwing yourself. So why not just say “screw statistics, I’m going with my gut”? Because there’s more at work than a choice between possible regret and ‘leaving the matter to fate’. There’s a moral imperative at work.

Why we are morally obligated to get vaccinated: Now, if everyone but one selfish guy gets vaccinated, then he will still be safe (because there’s nobody from whom he can catch the disease) and he has no risk of side-effects. So he gets all the reward without any of the sacrifice. That makes him a freeloader. It’s profiting from others’ misfortune. It’s cheating.

How good people avoid seeing this moral issue: If we can avoid the statistics and just say “vaccines are poison” then the vaccine looks worse than the disease it was meant to prevent. The moral/statistics problem is solved. Some people have heard that there is mercury in vaccines. That happens to be partially true for some vaccines. Mercury is not healthy. Thus the logic progresses.

But is mercury really so toxic? There is potassium in lethal injections and there is chlorine in bleach. Is potassium bad? Chlorine? No. Very different chemistry, scenario, concentration, etc. can give rise to wholly different levels of toxicity. Some mercury compounds are pretty nasty. Others are pretty benign. But gram for gram, there was more mercury in one salmon than was in the whole first-year vaccine course for an infant. And that was prior to it being removed completely in the last few years from infant vaccines.

In some other vaccines, there is a small amount of a mercury compound called thiomersal (not metallic mercury or methyl-mercury which are relatively nasty kinds). No mercury compound is good for you, but a little mercury-based preservative turns out to be statistically better than the risk of a bad batch of vaccine. Vaccines are made of protein – they are like broth. They will rot. Rotten vaccine is useless. Useless vaccine leaves you vulnerable to the disease that is supposed to be prevented.

A slight risk of low level toxicity is better than risking polio. The odds are still in your favor if you get vaccinated. But since there is a known risk (mercury!) versus an unknown risk (nobody gets polio any more, right?) people will be misled into false beliefs about relative risks.

The point is: this all comes down to statistics. We have to weigh the relative risks of a terrible disease becoming endemic again versus the risks of mass-scale injections. We have to weigh the risks of a trace quantity of mercury versus the risks of inactive or contaminated medicine. There’s math involved. And to someone who sees the world in terms of “us” and “them” – who sees Nefarious Motivations in the hearts of his fellow men – this can all look like obfuscation. I wish it were as simple as “it either works or it doesn’t” but in actual real life, things work with some probability, and weighing those probabilities is never an easy job.

Strangely enough, sound moral reasoning requires statistical analysis. And that puts us all at a disadvantage when trying to Do the Right Thing. Try telling someone that on Facebook. Or, for that matter, good luck getting your patient’s HMO to cover your time explaining all of that to your patient.

-Peter