claudine_c

[Yet another repost from my other blog. The serendipity-livejournal plugin has been unreliable lately.]

Vaccination has always been the subject of criticism and fear, and understandably so. The process of vaccination involves introducing a small dose of an infectious agent in order to protect individuals from harmful exposure to that same infection. This introduces the small risk that the infection may somehow mutate into a harmful version, giving the vaccinated person the precise disease against which they were supposed to be protected. In addition, the production and preservation of vaccines generally involves other substances being added, which may produce side-effects. Concerns are periodically raised about such side-effects, for example linking the oral polio vaccine with HIV, or various other vaccines with autism.

The vaccine-and-autism debate has recently been reignited in both the USA and the UK. A recent article by Robert F. Kennedy Jr in Rolling Stone and Salon concerns the use of thimerosal, a mercury-based preservative, in child vaccines against hepatitis B, haemophilus influenzae B (HiB) and diphtheria-tetanus-pertussis (DTP) in the 1980s and 90s. Kennedy’s article points to a conspiracy between the government and pharmaceutical companies to cover up the supposed link between thimerosal and autism. This article has a rather hysterical and paranoid tone and is scientifically questionable. Kennedy’s claims have been championed by anti-vaccination activists and condemned by sceptics, and struck fear into the hearts of previously unsuspecting parents. One of the more substantial critiques of Kennedy’s article appears in the “Orac Knows” weblog and is summarised in this post.

As a public health student who works with epidemiologists and has had some exposure to that discipline, I find the defence of vaccines made by scientists and public health officials more credible than Kennedy’s claims. Kennedy does not actually explain how mercury is supposed to cause autism, and indeed the only “evidence” cited is temporal coincidence: the fact that the number of autism cases increased following the introduction of thimesoral into vaccines. The increase in cases is an increase in diagnoses, and could be attributed to more sensitive diagnostic procedures as well as an actual increase in cases. (We may never know the “true” number of cases of any illness; we can only count those who are actually diagnosed.) In the absence of a credible causal link between mercury and autism, this temporal coincidence can only provide a suggestion, not proof, that there may be some association between the two.

The mercury-and-autism theory is not new. In the UK, mercury is a component of the measles-mumps-rubella (MMR) vaccine. Earlier this year, the BBC’s Horizon programme ran a story on the association between the MMR vaccine and autism. A British study in 1998 had started the controversy over mercury and autism in that country. This controversy is still a hot topic in the UK, as evidenced by the Horizon programme and by books such as A jab in the dark by a former editor of the British Medical Journal, Richard Horton.

When adversity strikes, it is understandable that we try to find something or somebody to blame. In the case of infectious diseases, it is usually possible to identify the actual infectious agent (a virus or bacterium) and perhaps explain how the affected person came into contact with it. It is more difficult to identify a specific cause of a behavioural or mental condition. This explains why some people affected by autism might welcome any suggested association between autism and a specific, easily identifiable cause such as mercury or a vaccine. But autism doesn’t yet have an easy explanation, and blaming vaccines runs the risk of allowing vaccine-preventable diseases to re-appear while contributing little to the search for an explanation for autism.

For over two hundred years, vaccines have helped reduce the number of people afflicted by debilitating and sometimes fatal infectious diseases. However, vaccination, by its very nature, introduces some risk of infection or side-effects that can be as devastating as the diseases they prevent. The decision to vaccinate or not to vaccinate must involve a comparison of the risks posed by one disease or another. It is quite a burden for a parent or nurse to have to make this assessment on behalf of a child who doesn’t understand the risks. To help us make these decisions, we need informed guidance based on scientific evidence as well as personal experience. Hysterical conspiracy theories and patronising denunciations of “pseudoscience” only raise the emotional level of the debate without contributing much substance.

[I wrote this for Blogcritics in response to some posts on the Blogcritics mailing list, but it was Matt McIrvin who first drew my attention to the Kennedy article.]