There is perhaps no issue in modern medicine that is as contentious as childhood vaccination. On one side are the doctors, scientists, and public health officials who argue that an overwhelming amount of evidence indicates vaccines are safe -- and that vaccine-preventable diseases like measles, Hib, and whooping cough are just as dangerous and deadly today as they were decades ago. On the other side are the parents who point to their personal observations to support their belief that vaccines cause or contribute to developmental disorders like autism.
I've spent more than two years researching this debate. After reading hundreds of papers, reviewing dozens of court cases, and interviewing people on three continents, I concluded that there was no reliable evidence supporting a link between childhood inoculations and developmental disorders. That raised a whole new set of questions: Why, despite all the evidence to the contrary, do so many people remain adamant in their belief that vaccines are responsible for harming hundreds of thousands of otherwise healthy children? Why was the media so inclined to air their views? Why were so many others so readily convinced? Why, in other words, are we willing to believe things that are, according to all available evidence, false?
If you assume that human beings are fundamentally logical creatures, this can seem like an impossible question to answer. But when it comes to decisions around emotionally charged topics, logic often takes a back seat to what are called cognitive biases -- essentially a set of unconscious mechanisms that convince us that it is our feelings about a situation and not the facts that represent the truth.
The origins of many of these traits can be traced back to the primitive conditions in which they were selected for millennia ago. Take pattern recognition, which evolutionary biologists like to explain through fables about our ancestors: Imagine a primitive hunter-gatherer. Now imagine he sees a flicker of movement on the horizon, or hears a rustle at his feet. Maybe it was nothing -- or maybe it was a lion out hunting for dinner or a snake slithering through the grass. In each of those examples, the negative repercussions of not taking an actual threat seriously will likely result in death -- and the end of that particular individual's genetic line. On the other hand, the repercussions of bolting from what turns out to be the shadow of a swaying tree or the sound of a gentle breeze will likely be nothing worse than a little extra exercise.
Unfortunately, a byproduct of that protective instinct is a tendency to connect the dots even when there are no underlying shapes to be drawn, and when our yearning to feel in control and our ability to recognize randomness are in conflict, the urge to feel in control almost always wins. This helps explain why it can be so difficult to demonstrate to someone that their initial read on a situation -- their instinct, their gut reaction, their feeling -- is, in fact, wrong. They also show why two reasonable, intelligent people who disagree can be equally certain that the evidence supports their understanding of the "facts."
It's at this point that confirmation bias, the granddaddy of all cognitive biases, kicks into action -- which is to say, it's at the precise moment when we should be looking for reasons that we might be wrong that we begin to overvalue any indication that points to our being right. Misapprehensions about medicine are particularly vulnerable to the effects of confirmation bias, because the process by which a given intervention works is so often contra-logical: It makes no intuitive sense that re-breaking a bone would help a fracture to heal or that using chemotherapy to kill living tissue would help a person survive cancer. Now consider vaccines. Injecting a healthy child with a virus in order to protect him from a disease that has all but disappeared just feels somehow wrong. The fact that getting vaccinated is so obviously painful and that infants can't understand that you want to help and not hurt them only makes matters worse.
Within minutes of the horrific events in Arizona this week, commentators began debating whether the hyper-partisan, at times ugly, rhetoric that's marked political debates of the last several years played a role in the shootings. It's a valid discussion to have: The fact that I'm a First Amendment hard liner has no bearing on my belief that we have a responsibility to consider how our words and actions affect others -- or society at large. But what is it, exactly, that we have to take responsibility for, and how do we do it?
Last week, the British Medical Journal published a report that accused Andrew Wakefield, the British researcher whose 1998 paper sparked the panic over the three-in-one measles-mumps-rubella vaccine, of deliberate fraud. I appeared on the press several times to discuss the issue -- and within twenty-four hours, I had received the following emails:
"Maybe you'll end up with an autistic child and find yourself thinking twice about your blubbering comments."
"You are nothing but a big pharma puppet. You are a scum bag. You treat our children like garbage. Makes me sick....We are amongst the strongest, most determined on earth. We KNOW what happened to our babies. We've lived it, we've seen it, we've researched it and we're certainly NOT going away."
"The Bible is very clear on such subjects, 'vengeance is mine says the Lord'. 'I will repay!'"
"At the end of the day you have to ask yourself, Would I give these to MYSELF? (Shame on you for DOING IT to your child)....Enjoy your life and I hope your child is one of the lucky ones not effected by these drugs....YOUR THE BIGGEST IDIOT in that room with THE MOST DANGEROUS perception."
The comments that appeared on vaccine-obsessed blogs were, if anything, even less restrained. This type of vitriol owes less to cognitive biases than to the increased polarization that inevitably results from surrounding yourself with like-minded people. (Think about the red-meat frenzy of the quadrennial Democratic and Republican conventions or the sign-waving mania churned up by a Tea Party rally. Or, to come at it from a different angle, consider what happens when a bunch of otherwise reasonable Red Sox fans get together to watch a baseball game in a bar: It's a fair bet that nobody's going home that night feeling any warmer towards the Yankees.)
This us-versus-them dynamic has become so ubiquitous because the mechanisms that have historically allowed for easy access to moderate positions are rapidly disappearing. Twenty years ago, it took a fair amount of effort to create an information cocoon: In 1987, nearly three-quarters of Americans tuned into a nightly news broadcast from one of the three networks, creating a sort of national common denominator for information about the world. Now, that figure has fallen below one-third, as consumers abandon the presumed neutrality of the networks in favor of cable news telecasts that gratify viewers by feeding them exaggerated versions of the opinions they already hold. An even more potent force in this regard is the Internet, where it's easier than not to fall down a wormhole of self-referential and mutually reinforcing links that make it feel like the entire world thinks the way you do. The anonymity and lack of friction inherent in the online world also means that a small number of committed activists -- or even an especially zealous individual -- can create the impression that a fringe viewpoint has broad support.
When dealing with debates that hinge on the interpretation of facts -- Are April snowstorms a sign of global warming or the opposite? Are the latest unemployment numbers a sign the administration's policies are succeeding or failing? -- these differences of opinion can quickly become personal: If someone sees black where we see white, it's hard not to assume that there's something about them -- either they're ignorant, or their emotions have the better of them, or they're lying in the service of a more base interest -- that prevents them from acknowledging what to us is self-evident. When looked at through this light, the seemingly contradictory ideas that have defined the vaccine wars begin to make more sense.
But it's time for everyone -- those who support vaccines and those who believe there's a conspiracy to hide their dangers--to dial things back and understand what we have in common: We all want to protect children. I know as well as anyone how easy it is to fall short: When I feel threatened, and especially when I feel my son's well-being is at stake, it's hard not for me to get a little bit crazy. But accusing my opponents of stupidity or ulterior motives is not simply wrong, it's a self-defeating error that ultimately makes it much harder for them to understand me, and for us to find common ground, in the future.
This post is adapted from Mnookin's new book, The Panic Virus: A True Story of Medicine, Science, and Fear.
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Seth Mnookin is a contributing editor at Vanity Fair and the author of The Panic Virus: A True Story of Medicine, Science, and Fear. His two previous books are Feeding the Monster, about the Boston Red Sox, and Hard News, about the New York Times. He blogs at SethMnookin.com, and you can follow him on Twitter at @sethmnookin.