Gardasil’s combo of sex and cancer must be irresistibly attention-grabbing. Campaigns promoting the genital wart virus immunisation have scooped advertising industry awards and have been stunningly successful at creating public, media, professional and political pressure for vaccination, as per this recent report in The New York Times.

Governments around the globe have been wooed and wowed, rushing to pay for the expensive vaccine with billions of dollars diverted from already-stretched public health budgets. This has been a remarkable act of faith because significant uncertainties remain over Gardasil’s cost-effectiveness.

It is well known that Gardasil works best in virgins but here is a question the advertisements never answer: how many 12-year-olds need vaccination to prevent one from eventually getting cancer of the cervix?

Various estimates exist. The lowest I have seen came from an author with documented competing interests including acceptance of grants from Gardasil’s manufacturer.

His answer, in a February 2008 Canadian Family Physician article written to promote the vaccination, was 276 girls. In other words, at best it seems there is about one chance in 250 that vaccinating a virgin will prevent that individual from getting cervical cancer (although, on the plus side, the vaccine should also confer benefits like preventing visible warts and abnormal pre-cancerous smears).

Further calculations were published last year in the Canadian Medical Association Journal. These suggested that if the vaccine does not confer life long protection and wanes by 3% per year with no booster being given, then over 9,000 girls need vaccination to stop just one from getting cancer.

Yesterday another piece of information was added to the jigsaw. The New England Journal of Medicine (NEJM) published estimations of Gardasil’s cost per Quality Adjusted Life Year (one QALY is one year of life in good health). A cluster of figures were calculated, some disappointing for Gardasil’s manufacturers.

Even in a wealthy country, spending over $US100,000 per QALY is widely regarded as unacceptable value for public money. Gardasil’s cost-effectiveness ultimately hinges on several unknowns including its duration of effect.

The NEJM article’s bottom line is that if the initial vaccinations confer lifelong immunity, then immunising 12-year-old girls seems cost-effective but immunising 26-year-old women does not. The Australian government funds the vaccine for 26-year-olds.

If, however, Gardasil’s effect wanes after 10 years — and this is entirely possible — then even vaccinating 12-year-old girls starts looking like poor value for money.

In developed countries, cancer of the cervix is a very unusual cause of death in women who get regular Pap smears. Nonetheless, I have watched a couple of patients die nasty deaths from it and I do encourage my eligible patients to get their tax-payer funded shots.

In fact, after personally prescribing about $100,000 worth of Gardasil, I am rather disappointed that I have not been offered any industry-sponsored junkets. Instead, the Australian manufacturer thinks my opinions on the drug’s marketing are unprofessional, inappropriate, incorrect and misleading. At least, that is what they once told my university’s Vice Chancellor. C’est la vie.