How do you Know if Your Bullet is Magic?

This cluster of attractive scientists is highly significant.

Against all odds I actually managed to see a movie the other night, and that movie was Contagion. It’s a solid flick, and I do recommend it. Even if you know kind of a lot about viruses, you will not be annoyed. They get almost everything right, and the Infectious Disease 101 exposition is not too disruptive. But they got one very important thing wrong, namely the point of human subjects research. Spoilers are about to commence below the jump.

Contagion boasts not one but two characters who use themselves as proverbial guinea pigs. As a novel virus ravages the globe, Alan Krumwiede (Jude Law) is a mustache-twirling villain who gets rich off of a sham cure. Specifically he films himself taking the cure and then recovering, sparking a global outcry for his homeopathic treatment, but we later learn he never really had the virus.

Then we have Ally Hextall (Jennifer Ehle), a heroic microbiologist who injects herself with an experimental vaccine that ultimately saves the rest of the world. Earlier in the film she has been lamenting how long it takes to develop a vaccine, one of the stated obstacles being human trials. That, presumably, is her motive for injecting herself, to speed up the approval process. The film seems to suggest that it worked, too, because the next thing we know the vaccine is in mass production.

Here’s why this is annoying. Let’s say I discover what I believe to be a cure for viral conjunctivitis. I get pink eye, then I take my treatment, then my pink eye goes away. My so-called experiment has proven exactly one thing: because I have not died, we can conclude that my treatment is less than 100% lethal. There is no way to know whether my treatment had any effect on my pink eye, because pink eye goes away on its own (remember Rooster Syndrome?). In the world of Contagion, 3 out of 4 people who get the virus recover. So even if the villainous blogger had really been sick, he could just as easily have perpetuated a fraud.

Same goes for the good doctor. She injects herself, she goes to see her sick father, and she does not get sick herself. But is her immunity a consequence of the vaccine? The only way to know for sure is to get in a time machine, go back to the moment of injection, give her a placebo instead, and see if this time she gets sick. This is what epidemiologists refer to as the counterfactual scenario, and obviously it exists only in theory.

In practice, you have to do the next best thing, which is those pesky human trials. You compare two groups of people who are as similar as possible to each other and as representative as possible of the people who would be using the vaccine. One group gets the experimental vaccine and the other gets something else. If the experimental vaccine group winds up with fewer infections and an acceptable number and type of side effects, we have a new treatment. If, on the other hand, they wind up being killed or otherwise seriously harmed by the experimental vaccine, then you’re damn glad you tested the vaccine before you started injecting it into everyone.

In the movie, Dr. Hextall invokes the Nobel laureate who gave himself H. pylori to prove that the bacterium causes ulcers. But surely the screenwriter Scott Z. Burns had another Nobel laureate in mind, namely Paul Ehrlich of Dr. Ehrlich’s Magic Bullet. I happen to love that somewhat flawed film, and this one is chock full of references to it, hopefully deliberate. The movie version of Dr. Ehrlich also tries to experiment on himself, and he refuses to allow his experimental treatment for meningitis to undergo a randomized trial, on the grounds that it would be wrong to withhold it from children. Luckily, both those treatments turn out to be effective and safe. You should see that movie, too, but bear in mind that it predates Mengele and Tuskegee before you draw any conclusions about the nature of research into human diseases (also watch out for orientalism and supportive wives).

In real life, there are no magic bullets. No treatment is 100% effective and no prevention is either, and that’s why it’s difficult, time consuming, and entirely necessary to test them with randomized controlled trials. I was disappointed that Krumweide turns out to be a con man, because I was hoping Contagion would dramatize how well-meaning people can cause serious damage by failing to understand epidemiology. When it comes to science, oversimplification is more dangerous than any movie villain.


One thought on “How do you Know if Your Bullet is Magic?

  1. Pingback: The Epidemiology of Abortion: A Primer | Worse for the Fishes

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