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Bachmann and HPV: the danger of speculation over evidence

Peter Gill
Last edited 16th September 2011

This week brought back fears from a decade ago. Michele Bachmann, a US Republican presidential candidate, claimed that the HPV vaccine was a "very dangerous drug" that could lead to "mental retardation".

HPV or human papillomavirus is a virus that is associated with the development of genital warts and cervical cancer. Just this week, the Lancet reported that the global cervical cancer rates have increased over the past 30 years to 454,000 cases in 2010.

Clearly cervical cancer is an issue that cannot be ignored. Vaccines against HPV are life-saving.

Bachmann’s claims drew a sharp response from the American Academy of Pediatrics who stated that her comments have “absolutely no scientific validity.” To date over 35 million doses have been administered in the US with an excellent safety record.

Why did she bother to meddle with science? The answer is deadly simple: politics. Republican rival Rick Perry issued an executive order requiring girls in Texas to get the HPV vaccine in 2007. In a heated debate, Bachmann suggested that the decision was made in return for political donations from Merck, the manufacturers of Gardasil (the HPV vaccine used in the US).

Conflicts of interest are a separate issue; the focus here is on science.

The concern amongst health care professionals is the damaging impact false claims have on vaccination rates. The perceptions of vaccines changed forever after a now retracted article was published in the Lancet in 1998. In this small study of 12 children the now-disgraced British doctor Wakefield linked the Measles Mumps and Rubella (MMR) vaccine to autism. The media coverage and speculation that followed led to UK vaccination rates dropping to 80% in 2003-4.

Vaccine fears have fueled the recent outbreaks of measles. Before the MMR vaccine, measles was thought to be “as inevitable as death and taxes”, mumps infection could lead to sterility in post-pubescent boys and pregnant women that contracted rubella had children with serious congenital defects. The MMR vaccine was a public health success before Wakefield.

Politicians can throw mud at each other all they like but when they enter the ring of public health, they jeopardise putting all our health at risk. Society cannot let another vaccine crisis strike.

A US bioethicist has stepped forward and offered $10,000 to Bachmann’s charity of choice if she can prove a claim that the HPV vaccine caused mental retardation. Will she take on the challenge? For the sake of public health, hopefully not.

autism and brain scan test: the real predictive value

Carl Heneghan
Last edited 11th August 2010

A brain scan that detects autism in adults could mean much more straightforward diagnosis of the condition, scientists say. Reported the BBC, Sky the Guardian and many more.

I had great difficulty getting hold of this paper, it wasn’t published online at the time of the press release. I managed to get a copy via Ben Goldacre at Bad Science and Evidence Matters who sent me the full text. Given this problem in getting the paper, it is highly likely no one who released the story has actually read the paper.

The news all report the headline ‘The researchers detected autism with over 90% accuracy, the Journal of Neuroscience reports.’

Sounds impressive, but this is one of the most obvious mistakes to make in interpreting a diagnostic test result. Never mind this is not the correct study type.

What has happened is the sensitivity has been taken for the positive predictive value, which is what you want to know: if I have a positive test do I have the disease?

Sensitivity: The proportion of people with disease who have a positive test.
Positive predictive value (+PV): The proportion of people with a positive test who have disease.

So, for a prevalence of 1% the actual positive predictive value is 4.5%. That is about 5 in every 100 with a positive test would have autism. Even at a prevalence of 2%, only 8.5% would be correctly identified.

Suddenly, not that great a test. This has to be one of the worst examples of misinterpreting diagnostic test results in the media I’ve ever seen.

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