Bob Bury

Do you chance it...?

This is the fourth article I've contributed to this site, and looking back, the other three have all dealt in some way with the concept of risk.

So I'm feeling less than original in returning to the topic in this column. But I think I'm justified though. If you look at the 'hot' scientific topics in our newspapers, certainly in the UK, most of them involve some discussion of risk, and nearly all of them display a misunderstanding of the principles underlying risk assessment, and a touching faith in the ability of scientists to banish danger from our lives.

MMR - safe or not ?
Take the recent and continuing debate over the safety of the MMR (measles, mumps, rubella) vaccine in the UK. Our children, like those in most of the 'developed' countries, routinely receive the vaccine, and as a result, outbreaks of these three potentially serious diseases are now a rarity. Then a couple of years ago, a paper appeared in The Lancet suggesting that the vaccine might be linked to the development of autism and inflammatory bowel disease in children. There were a number of weaknesses in the paper, which only looked at a relatively small number of cases, and much larger surveys have consistently failed to support the author's contention of any link between vaccination and these diseases. But that doesn't stop ill-informed comment in our media. Just this week, the Yorkshire Evening Post reported the case of a young child who had suffered a supposed reaction to the vaccine, and the editorial comment was interesting, because it made explicit an assumption which underlies much of the media comment on issues like this. The writer demanded that we should be able to assume that any treatment used on patients is 100% safe.

How does science assess risk ?
Sounds reasonable enough, doesn't it? But we don't demand such high levels of immunity from risk in any other aspect of our lives. We are prepared to accept quite high levels of danger in every day life, especially if we get some pleasure from the activity concerned (smoking; drinking alcohol; skiing; white-water rafting for example). So why demand absolute safety in medical treatment? And the really interesting question is this: even if we agreed that it was reasonable to demand such a guarantee, could science provide it? For non-scientists, the slightly surprising answer is that it is not possible to prove anything scientifically. Science works by setting up theories to explain the observed facts, and then devising experiments to test those theories. It doesn't matter how many times an experiment produces a result which confirms the theory, there is always the possibility that the next one will produce a contrary result that blows it out of the water and sends you back to the drawing board. However, the more often that experiments uphold a theory, the more likely it is to be true, and there comes a point where the weight of evidence is such that we are forced to accept the truth of a particular explanation of the facts. In other words, although we can never prove something to be true, it is possible to fail to debunk it so often that it would be perverse not to accept it as 'proven' scientific fact.

So where does this leave MMR ?
So where does this leave vaccination with MMR? Parents are in a difficult position. Like our editorial writer mentioned above, they want to be assured that anything they expose their children to is absolutely safe. We've seen that we cannot give them that assurance for MMR, or for anything else. However, millions of children have now been vaccinated, and the results demonstrate that vaccination is very much safer than not giving the MMR and allowing them to be exposed to the three diseases concerned. Which brings us back to the concept of relative risk. If you know that the risk from exposure to disease is very much greater than the risk from the vaccine, it should be easy. But we've been conditioned to accept the 'natural' hazard of disease, and to demand absolute safety from man-made medicines, and it's also true that the current generation of parents (thanks largely to vaccination) have forgotten how serious these childhood diseases can be. As a result, vaccination rates in many areas are falling to levels where epidemics of measles are likely to occur, leaving some children dead or irreversibly damaged. And all because our schools don't teach us how to assess risk.

- November 2004

About the Author

Consultant Radiologist