New research casts some doubts over the vaccine and vindicates a decision by Mary Harney not to approve a catch-up programme
RESEARCH INTO cervical cancer vaccination and an accompanying editorial, published today in the New England Journal of Medicine, highlight the intricate calculations and assumptions made by experts when they attempt to assess the cost-effectiveness of new health interventions.
Following on from the decision earlier this month by Minister for Health Mary Harney to green-light a national human papilloma virus (HPV) vaccination programme from September 2009, this latest research allows us to examine this policy decision through a lens of a different shade.
Public health experts from Harvard University in Boston used a complicated model to assess the health and economic implications of HPV vaccination.
Because this type of research involves looking to the future, certain assumptions must be made about the efficacy of a vaccine, its likely uptake by the target population, the cost of the vaccine and its safety.
Before making her decision, Ms Harney took advice from the Health Information and Quality Authority (Hiqa) which in turn asked the National Centre for Pharmacoeconomics (NCPE) to carry out a cost effectiveness study.
The assumptions made in this study included a vaccine uptake of 80 per cent, a vaccine efficacy of 95 per cent, lifelong protection against HPV infection from the three shot immunisation of 12-year-old girls. It also assumed the soon to be launched national cervical cancer screening programme would cover 80 per cent of eligible women.
But the Harvard researchers raise a number of questions: Will the vaccine ultimately prevent cervical cancer and lower deaths and not just prevent non-invasive forms of the cancer? How long will protection conferred by HPV vaccine last? Will there be a need for a 10-year booster injection? Will vaccination affect attendance at screening programmes when the adolescent girls reach their 20s and 30s?
In addition, the Norwegian editorial writer is concerned that the suppression of HPV-16 and HPV-18 (the desired effect of the vaccine) may allow other strains of the virus to grow instead. Could these other serotypes - there are over 200 HPV types in total - emerge as cancer causing agents in response to the eradication of types 16 and 18?
While the Harvard authors found that vaccinating 12-year-old girls was cost effective in an American context, the editorial suggest they may have been over optimistic in their basic assumptions.
"Whether these assumptions are reasonable are exactly what needs to be tested, in trials and follow-up studies. If the authors' baseline assumptions are not correct, vaccination becomes less favourable and even less effective than screening alone," the writer notes.
But this latest research is not all bad news. The Minister's decision not to approve a catch-up programme among 13 to 15-year-olds at a cost of €30 million is vindicated.
Although announced at the time as a decision prompted by budgetary pressures, Ms Harney made the right call, albeit for serendipitous reasons.
And it certainly does not imply that the NCPE/Hiqa report is flawed. The authors made certain assumptions, as they are required to do, as part of the health technology assessment. They were upfront about these assumptions and considered a large number of different scenarios. Just because the Harvard researchers question some of these assumptions does not make them wrong.
However, there are a number of caveats highlighted by the papers from this prestigious medical journal.
If the vaccine wears off after 10 years, then immunisation is less cost effective and screening for the disease using cervical smear testing may be more effective than catch-up vaccination programmes. And it is reasonable to question, although quite impossible to answer, how a vaccinated group of women will feel about cervical screening many years after they were immunised.
Perhaps the most important issue raised by the new research is an ethical one: would it be right to wait at least 15 years for answers to these issues, and to hold off making the breakthrough cervical cancer vaccine available to young women?