Post Hoc Ergo Propter Hoc

I got into a debate today on facebook about the safety and appropriateness of the anti-cervical cancer vaccines Gardasil and Cervarix, which made me want to explore more here. (Background: Cervical cancer is casued by certain strains of the Human Papilloma Virus, and by preventing infection with the virus people can be protected from the disease. It is not yet clear how long the vaccines provide protection, and they only work against certain strains of the virus, although this includes the ones responsible for most cancers.)

I should start off by saying a few things. One is that, as usual, I am no expert on this topic at all. The second one is that I have several biases that make me inclined to favour these vaccines. I try to put these aside for rational analysis, but I admit I might not have done so successfully. What are these biases?

Well firstly I am pro-vaccine in general. Our lives are now twice as long as our ancestors. There are three main reasons for this: Vaccinnes, clean water supplies, and everything else. I have never seen an estimate of the relative contributions of the three, but if vaccines are the smallest contributors it would not be by much. So we’er probably talking more than a dozen years on the average lifespan maybe more. Moreover, unlike some medical interventions, they give us good years, rather than keeping us alive when we might not wish to be. Of course that does not mean that every vaccine is good. Each needs to be assessed on its merits, but with so much good, and so little harm, behind them a new vaccine has an impressive heritage.

Secondly, I’m pro-Australian science. You can debate just how large the UQ contribution to these vaccines’ development was, but it was certainly big. I like seeing Aussie scientists come out ahead, and if Ian Frazer’s virus-like particles prove safe and effective they’re going to be one of the success stories of 21st century science.

Thirdly, part of the opposition to these drugs is simply appalling. Although HPV can be transmitted through mechanisms other than sex it is generally seen as an STD.  So some people think we should allow it to spread, in order to put people off having sex. My friend and business partner Charles Richardson put it better than I could, back in 2006:

A team led by Australian of the year professor Ian Frazer has developed a vaccine against the viruses that cause most cases of cervical cancer.
But [Senator Barnaby] Joyce and others are concerned about using it in case it “would promote teenage promiscuity.” According to The Australian, Joyce “said he would be ‘personally very circumspect’ about giving such a vaccine to girls who were too young to cope with the potential consequences of s*xual activity.”

Just think about what that means. These people are saying that teenage girls need to be scared off having s*x by the threat of getting cancer.
Not just that teenage promiscuity is bad – reasonable people can disagree about that – but that it’s so bad that cervical cancer is an appropriate punishment for it.

And they have the gall to call themselves “pro-life”?’

It is quite clear that some of the reports of negative reactions to Gardasil are coming from these forces, although others are picking up the meme and, well, transmitting it.

Finally, I’m aware of something most people engaged in the debate are not: HPV may be about much more than cervical cancer. There is evidence of varying strength linking HPV to a range of other cancers. Most of these are quite rare, but I’ve interviewed researchers who think HPV causes a substantial portion of breast cancers. Given how common breast cancer is, if the vaccine cuts rates here even slightly it will have a huge impact. The researchers suggested it is possible the vaccine will save more lives through preventing breast than cervical cancer. There is a deep irony to this. Republicans in the US attempted to styme research funding for cervical cancer ostensibly because breast cancer should be the higher priority but really because, well see above. There was a marvelous episode of the West Wing on this.

Nevertheless, all that does not mean the vaccine is safe. Even really wonderful vaccines can sometimes have serious side-effects in a minority of cases, and sometimes these effects might be such that the vaccine should be withdrawn, or at least come with a warning.

The problem is that some people do get sick, and it’s natural to look around for a source. People who have been injected with a new vaccine not long before are likely to blame it, which is where the title of this post comes in. The Latin phrase means “This came before that, so therefore this caused that“. I’m not sure if the Romans used it ironically, but that is certainly the preference these days.

For the individuals involved it’s understandable. A friend of mine has been stricken with a terrible disease, so unusual the doctors are not sure what it is. At first they thought it was MS, but since it seems to be improving they’re now edging towards an unusual form of chronic fatigue. She’s sure a Gardasil shot a couple of weeks before is the cause, and is suing. She’s part of a class action, and unlikely to be the only one. However, with 40 million doses it’s hardly surprising there would be a few people struck down by odd things shortly after being injected. Another friend of mine has somewhat similar (indeed worse) symptoms, and got them before either drug was even being tested. People have been getting odd diseases long before vaccines, the question is whether they are now getting them more often.

We already know Gardasil and Cervarix can cause Guillain-Barre syndrome at a rate of a few every hundred thousand doses, and more minor effects such as temporary dizzyness and sore arms are much more common. If there are other side effects we need to know, and that is where VAERS comes in (Australian names vary by state). The idea here is that whenever a doctor sees a patient who has recently had a shot, and there is the slightest possiblity whatever ails them could be the result of the vaccine he or she is supposed to report it. Epidemiologists can then examine the data to see if any conditions are turning up more frequently in the recently vaccinated than the rest of the community.

It’s been claimed to me that doctors are reluctant to report cases to VAERS because “it might be caused by something else”. If so they are probably not good doctors. The whole point of VAERS is that everything on a long list of symptoms is to be reported. In most cases something else will have caused it, but only by getting a very large sample size can we work out whether there is a statisically significant association with the vaccine.

I have no idea how well doctors are doing in reporting the effects they should be, but unless the underreporting really is chronic the evidence suggests the risks from these drugs are far below the benefits.

If anyone has been affected by the vaccine they deserve compensation. I’d prefer to see this through a national no-fault disability scheme, but until that longed-for day, I’ll take a system for taxing manufacturers to create a fund for such cases. But that is no reason to put the lives of hundreds of thousands of women at risk by leaving them exposed to a disease we can stop.

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About Stephen Luntz

I am a science journalist, specialising in Australian and New Zealand research across all fields of science. My book, Forensics, Fossils and Fruitbats: A Field Guide to Australian Scientists is out now through CSIRO Publishing. I am also a professional returning officer for non-government organisations. I'm very politically active, but generally try to restrict this blog to scientific matters.
This entry was posted in Enemies of science, Hope, medical science, Science policy. Bookmark the permalink.

One Response to Post Hoc Ergo Propter Hoc

  1. Pingback: The Disease That Never Happened | Forensics, Fossils and Fruitbats

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