Vaccines, Autism and Perception of Risk

This week’s New Scientist contains the first major discussion of the Autism Omnibus Proceedings that I have seen in the UK media. There are a few minor inaccuracies. For example the Omnibus is not just about thimerosal. There are three theories of general causation proposed by the Petitioners Steering Committee: thimerosal; MMR; thimerosal and MMR combined. And the case of Michelle Cedillo  with which the proceeedings have opened is based on the final hypothesis, that thimerosal containing vaccines administered in the first year of life damaged her immune system to such an extent that the MMR caused her to become autistic.

Leaving aside the particulars of  individual cases the New Scientist makes some important points. After outlining the preponderance of scientific opinion  against thimerosal as a causative factor in autism the New Scientist editorial goes on to say,

On the surface then, this looks like a battle between the reasoned arguments of experts and irrational parents. This is how health officials have interpreted vaccine disputes in the past, but in so doing they alienated the people they are meant to be advising.

In the UK, a similar debate kicked off in 1998, when scientist and doctor Andrew Wakefield cast doubt on the safety of the measles, mumps and rubella (MMR) vaccine. The response of the medical establishment was well intentioned but disastrous. Experts met behind closed doors and emerged to tell the public the vaccine was safe. Leaflets gave celebrity endorsements of MMR. Rather than examine Wakefield’s claims, which were shaky at the time and are now widely discredited, the government merely told parents not to be silly. Not surprisingly, parents did not buy it. Take-up of MMR fell from 92 to 82 per cent, close to the minimum level needed if isolated cases are to be prevented from developing into epidemics.

At the time of the MMR crisis I remember feeling patronized and my intelligence insulted by what seemed like another attempt to replace serious debate with a public relations spin job by the government and their officials. They made me want to believe Wakefield. And for a while I very nearly did. 

Let me be clear. I am not denying. that a small number of children do have adverse reactions to vaccines, sometimes with disasterous consequences. But prior to vaccines every child had adverse reactions to the diseases we vaccinate against and many of the outcomes were tragic. I speak as a survivor of measles, mumps and whooping cough. Today’s parents may be forgiven for failing to appreciate just how serious these diseases can be. The very success of the vaccine programme has led to complacency in this respect.

It has also contributed to the high level of risk aversion in the affluent societies of the world. In my grandparents time it was expected that some children would die. Around 100 years ago infant mortality rates in the USA and the UK were horrendous. One in ten children died before their first birthday. That would put the UK and the USA in the top ten for infant mortality today ahead of countries like Ethiopia and Sudan.

Vaccination rates have contributed to the steady decline in infant mortality. As it happens the current US figure of just under 7 children in a thousand for infant mortality is slighter higher than their rate for autism.

But parents do not consider statistical probabilities when making decisions about their child. When you sit in the doctor’s waiting room with a healthy 18 month old infant in your arms the chances of them dying in infancy are miniscule compared to the chance that they might develop autism. And if there were the tiniest doubt in your mind about the safety of childhood vaccines you would walk out of that waiting room.

In reality most parents have vaccinated their children with overwhelmingly positive outcomes. But for a minority of parents the doubt has been planted post hoc and some of them have thus been led into the logical fallacy of post hoc ergo propter hoc and blame the vaccines for causing their child’s autism.

The New Scientist suggests that the way to avoid this in the future is for scientists to be

open, and admitting what science does not know. It takes time and effort, but the alternative is that parents and health officials talk past each other.

I can see their point. For a long time science has been presented as the infallible source of truth, not by scientists but by opinion makers in politics and the media. A minority of scientists may have been seduced by this and others have challenged it. But I suspect that most have got on with the job, oblivious to the impact that reports of their work have on public opinion.

However, I am not convinced. Most people’s perceptions of science are not based on what scientists say, but on media reports of what they say. And the standards of science reporting in the popular media are frankly terrible.

This is caused by a mixture of ignorance and laziness that even affects magazines like New Scientist, for whom scientific ignorance should not be an issue. Yet too often they carry short reports based on pilot studies that are not yet ready for public consumption. These are then picked up by the non-scientific media and presented as “proof positive” when no such proof exists.

As an example of laziness, their main article on the Autism Omnibus proceedings contains a reference to mercury as “a known neurotoxin.” Amongst the anti-vaxers this carries the subtext, “They knowingly injected a neurotoxin into our children.” They did it on purpose, dammit!

Is there any circumstance in which New Scientist reporters would describe a substance as an unknown neuro-toxin? The phrase, known neurotoxin, is  code for a whole set of assumptions to which New Scientist certainly does not subscribe, but to which it gives unwitting approval by the careless use of language.

Overall, the New Scientist coverage is informed by support for the standards of scientific proof and rigorous criticism for those who fall short of those standards. At the same time it respects the sensibilities of those for whom autism and its causation is not primarily a discussion of scientific principle but a very personal and immediate issue. This discussion has focused primarily upon the issues raised by the New Scientist editorial. I hope to return to the substantive article tomorrow.