Falsehood flies and the truth comes limping after; so that when men come to be undeceived it is too late: the jest is over and the tale has had its effect. - Jonathan Swift

The tale of childhood vaccines and autism is a sad one. Even though there is now a large bulk of excellent scientific evidence that MMR does not cause autism, it is too late. The story is out and the damage affects the credibility of the vaccine. The immunisation rates drop, the disease comes back and our children suffer.

This article responds to the Dialogue view expressed by Barbara Sumner Burstyn (June 24). I am saddened to see how a call to be more honest with scientific knowledge has degenerated into slander and name-calling.

My concerns have been directed to health professionals to consider the accuracy of the information they are distributing. What midwives recommend to patients should have a basis in science.

Science is not truth - it is a tool using an accumulation of knowledge to build a verifiable body of knowledge. It is the foundation on which our practice of medicine is based.

We all know there have been errors in medicine, and there will be again. But while acknowledging the limitations of science, we can recognise the tremendous gains.

Control of infectious disease means we do not expect our children to die or be maimed from vaccine-preventable diseases.

Immunisation is universally acknowledged as one of the greatest advances in science, and its achievements are well documented - for example, the eradication of smallpox, the eradication of polio in the Southwest Pacific and measles eradication in many countries.

In the name of informed consent, a range of issues were expressed by Barbara Sumner Burstyn. These have no grounding in genuine scientific debate.

Informed choice needs to be informed.

I support the statement that we must lose blind reason. But when I look at statements which say vaccines cause SIDS, autism and Crohn's disease (good research shows they do not), we have moved into an era of blind faith in anything that is anti-science because all science must be faulty.

Is this just a new form of rigidity in a world looking for absolutes? We have probabilities, not absolutes. Why do we have to accept absolute statements that are incorrect disguised as informed consent?

It is not informed consent to tell parents there is thiomersal (mercury) in childhood vaccines; there is not. There used to be. It was used widely as a preservative. It has been phased out of childhood vaccines as better technology has developed.

Genuine informed consent would look closely at the rigorous double-blind controlled trials that are the benchmark of vaccine licensing and look at the quality of the trials. Genuine informed consent would not tell us they do not exist.

The Government uses these studies to assess the safety and effectiveness of vaccines before deciding to license a vaccine.

Surely genuine debate should be about the adequacy and quality of the evidence that is used.

Genuine informed consent cannot ignore herd immunity. Herd immunity is an old-fashioned term and is known more sensibly as community immunity. It is the principle that bugs circulate in communities.

The less immune protection in the community (either from vaccine or past disease), the more bugs. Hence more disease in that community.

There are many heart-rending examples of disease outbreak throughout the world when immunisation rates drop, such as whooping cough epidemics in the 1980s in Britain, Japan and Europe which caused many children to die. Even today measles outbreaks occur in pockets of unvaccinated populations in Holland.

Why can we not debate the quality of the science? Why this trendy need to deny there is research? Why treat the deeply held belief of some pseudo-scientist as fact.

Opinion is not fact. Fact is a painful, slow accumulation of knowledge through peer-reviewed, published research. Let's understand science with all its limitations and use it as the tool it is.

* Dr Nikki Turner is director of the Immunisation Advisory Centre.

* Rudman's City will return next Wednesday.