Population-based evidence for the preventative efficacy of quadrivalent HPV in Australia

The HPV vaccination programmes introduced by many countries over the last few years (since 2007) reveal considerable diversity in the coverage they have achieved, the mode of access (i.e. school, public health, private clinics) and responsibility for cost (i.e. publically vv. privately funded) – even in Europe (see ECDC Guidance).  In the light of the known efficacy of the vaccine, implementation has seemed frustratingly slow – partly, in some cases, due to ungrounded negative public perceptions around safety (e.g. in Japan where the national programme was actually suspended) and the impact on sexual mores (e.g. in the US).  Early indicators of its positive health impacts in countries like Australia – where implementation was early (2007) and wholehearted – are therefore to be welcomed, as favouring the implementation of programmes in the future.  In the absence of evidence of the reduction of cervical and other cancers, evidence of the effectiveness of the quadrivalent vaccine against warts – from clinics (STI/Donovan & Fairley; STI/Garland & Jayasinghe; STI/Fairley & Bradshaw), or pharmacists (STI/Wilson & Baker) – or evidence for the reduction of cervical abnormalities (STI/blogs/Brogly & Yang) – may offer a proxy.

Smith & Canfell (S&C), recently published in Journal of Infectious Diseases, claim to provide the first whole population analysis of the impact on genital warts of a national HPV vaccination programme – and this may be the best predictor of the longer-term, and more important, cancer prevention benefits to be seen in future years.  It is no surprise it derives from Australia, the first (2007) country to introduce routine school-based vaccination of 12-13 yr girls, plus catch-up through to 2009 for girls 13-17 yrs in schools, and young women 18-26 yrs in primary care. Earlier studies in Australia largely relied on data from sexual health clinics; this study is based on national data of all hospital episodes 1999-2011 involving a diagnosis of genital warts.

The findings of S&C show a decline of 89.9% in admissions involving warts from 2006/7 to 2010/11 for girls aged 12-17 yrs, a decline of 72.7% for women aged 18-26, and a decline of 38% for men aged 18-14 (the indirect effect of female vaccination).  The decline of cases in the 18-28 age group occurs from mid-2008. Other age groups do not show the same sharp decline, nor do MSM – to judge from the fact that the decline exclusively concerns warts in non-anal location.

An issue of particular concern to Australia, and one that consequently receives considerable attention in this study, is the impact on the indigenous population, where incidence and mortality rates for cervical cancer are, respectively, 2.8 and 4.7 times higher for the indigenous as for the non-indigenous population.  Reductions for indigenous and non-indigenous females appear to be similar (86.7% and 76.1% respectively) – which is curious, given that data for two Australian states indicate lower rates of course completion (3 doses) by indigenous females.  If the same tendency in uptake were replicated in the other Australian states (which we don’t know) this might suggest the efficacy of ≤2 dose courses of therapy.  Such a result would corroborate the findings of a recent study covered in this blog (STI/blogs/”Catch up” and incomplete HPV vaccination), which investigates the efficacy of ≤2 dose courses of therapy also in the context of socially disadvantaged groups.