Tuesday, February 9, 2010

Autism, Vaccines, and the Affective Response to Risk

In February 1998 The Lancet published a small paper by A. J. Wakefield, et. al., which studied 12 autistic children and found no link between their autism and the fact that the kids had received the measles/mumps/rubella (MMR) vaccine. “We did not prove an association between measles, mumps, and rubella vaccine and the syndrome described” they wrote.

But at the news conference announcing the findings, the lead author, Dr. Andrew Wakefield, suggested such a link, setting off a firestorm of fear that has had profound consequences for public health around the world, even for the public’s fading faith in science itself. The formal retraction of the paper by The Lancet Tuesday gives us a chance to step back and consider why this profound disconnect between our fears and the facts occurred, and the consequences, so we might think more carefully about risks moving forward.

Scientists think of risk as something measurable, quantifiable. To them, more probable = worse. But to you and me risk is more than a number. The Cambridge Dictionary defines risk as “the possibility of something bad happening.” Bad to you, and bad to me, can be very different things, at different times, under different circumstances. To us, it’s not just the probability of the unwanted outcome. It’s the nature of the badness too.

Humans have a powerful, complex system that helps us detect and respond to the possibility that something bad might happen. Most of this risk perception goes on below cognition, powered by ancient brain wiring and chemistry, and patterns of information processing, that rely on a host of subtle affective cues which help our brains instantly gauge whether some sight or sound or smell, or idea or memory, holds potential danger. The system rests on a hair wire trigger set to react to potential threats instinctively, before the cognitive parts of our brain even have a chance to get the information and think it over. And in the ongoing risk response that follows, emotions and instinct continue to have the edge over reason and purely fact-based rationality. As Joseph LeDoux, a pioneer in the neuroscience of fear, wrote in The Emotional Brain, “…the wiring of the brain at this point in our evolutionary history is such that connections from the emotional systems to the cognitive systems are stronger than connection from the cognitive systems to the emotional systems.”

One of the affective cues that will set off this system is a risk to our kids. (Look at our excessive fear of child abductions.) Wakefield’s suggested link between MMR vaccines and autism certainly tapped that sensitivity, especially among parents with autistic kids who hope that knowing the cause might afford a cure.

Another cue is trust. If we trust the people and institutions that are supposed to protect us, we will be less afraid. If we mistrust them, the same warning signal will set off a stronger more protective risk response. In Europe, where Wakefield’s intimations about MMR vaccine took off, they came against a backdrop of Mad Cow disease, controversy over the safety of genetically modified foods, and several other issues that had already begun to shake public trust in science and the public health institutions of government. So since Wakefield, as scientists have tried to explain the overwhelming evidence that refutes the connection Wakefield suggested, the problem hasn’t been the evidence. It’s been lack of trust in the institutions that develop and deliver that evidence.

Lack of trust, and a threat to our kids, were just two of many affective factors that contributed to the response to Wakefield, parts of a survival system that relies on facts and feelings, cognition and instinct. We should be grateful to this system. It’s worked pretty well, so far. But a system that evolved to respond instinctively to threats like guys with clubs, and snakes, and the dark, and which still gives the edge to affective cues over hard facts, can serve us poorly when more complex modern risks like vaccines, or climate change, or mercury in seafood come along. Responding affectively to threats that aren’t as obvious, that require a little more analysis, which involve tradeoffs, can get us into trouble.

Vaccination rates in many places are down, in some places below the ‘herd immunity’ level necessary to keep an infectious disease from spreading. In many places, measles is staging a comeback (and in some places, it’s killing kids). Resistance to many other vaccines has also risen. Tens of millions of dollars has been spent researching what science already knew - and what indeed Wakefield’s paper actually reported - that the link between MMR vaccination and autism that so understandably evokes fear in parents of autistic kids, isn’t there. And the continuing controversy, fueled by a 24/7 “He Who Screams Loudest Wins” media age, feeds a growing mistrust in the scientific community that provides precisely the kind of expertise we don’t have as individuals, and which we need to figure these things out for us.

We can’t undo the affective risk response system. It’s deeply wired into us. But in the name of all our health, we need to understand it better, honestly recognize the harms it can do, and factor an appreciation for the dangers of how we react to risk into the choices we make, as individuals, and as a society. That way those choices will not only feel right, but stand a better chance of doing us the most good.

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