ArticlesEarly effect of the HPV vaccination programme on cervical abnormalities in Victoria, Australia: an ecological study
Introduction
Since the first prophylactic vaccine against human papillomavirus (HPV) was licensed in mid-2006, the quadrivalent vaccine (which provides protection against high-risk HPV types 16 and 18, and low-risk types 6 and 11, which cause 90% of genital warts) or bivalent vaccine (targeting HPV types 16 and 18) have been implemented in more than 28 countries as part of their national immunisation programmes and implemented at a sub-national level through donations in at least 17 developing countries.1 Persistent infection with high-risk genital HPV types is needed for the development of cervical cancer, and HPV types 16 and 18 are detected in 70% of cervical cancers, half of high-grade cervical abnormalities (HGAs), and a quarter of low-grade cervical abnormalities (LGAs) worldwide.2 Although the target age groups vary in different countries, the vaccine is aimed mainly at girls between the ages of 9 and 12 years because it is most effective when given before the onset of sexual activity, because it has no effect against HPV infection—which is transmitted sexually—once it has been acquired. Various countries have also chosen to implement short-term catch-up programmes aimed at older age groups, ranging from 13–18 years to 26 years.3
Australia was the first country to roll out an extensive, funded national HPV vaccination programme with the quadrivalent vaccine GARDASIL (Merck, Whitehouse Station, NJ, USA) in April, 2007, within the context of an already intensive and successful national cervical screening programme. The vaccination programme consists of a continuing component that targets 12–13-year-old girls in schools and two catch-up programmes, one for 13–17-year-old school girls, and one for 18–26-year-old women through general practice and community settings delivered between July, 2007, and December, 2009. In Victoria, the second most populous Australian state, the HPV vaccine programme in secondary schools began on April 16, 2007. Girls in school years 7 (ages 12–13 years), 10, 11, and 12 (ages 15–18 years) were offered vaccination in 2007, with the remaining two catch-up cohorts (aged 13–14 and 14–15 years in 2007) offered vaccine in 2008.4 Vaccine coverage estimates from the National HPV Vaccination Program Register for the school programme in Victoria show a three-dose coverage of 79% in first-year high-school students and 71% in final-year high-school students.4 A population-based telephone survey done in Victoria in early 2009 noted self-reported coverage rates of 74% for one dose, 69% for two doses, and 56% for three doses in young women aged 18–28 years.5 These data indicate that the programme probably achieved high coverage.
Australia's HPV vaccination programme includes the broadest funded catch-up age range in the world3 and overlaps with the age cohort presently eligible for cervical screening in Australia. The National Cervical Screening Program policy recommends one cervical cytology test every 2 years, beginning at age 18 years (or 2 years after onset of sexual activity, whichever is later) until age 69 years. The National Cervical Screening Program was established in 1991, and since that time both cervical cancer incidence and mortality have halved.6 Participation rates in the programme are 61·2% of women every 2 years, 73·9% every 3 years, and 86·3% every 5 years.7 Monitoring of the early effect of the vaccine in Australia is helped by the existence of state and territory Papanicolaou (Pap) test registers that record nearly all cervical cytology and histology results and the National HPV Vaccination Program Register, which was established to support and monitor the HPV vaccination programme.8
A rapid effect on infection with vaccine-targeted HPV types is predicted after the implementation of population-based HPV vaccination programmes.9 Indeed, early data from sexual health clinics in Australia suggest that the incidence of genital warts in Victoria began to decrease in the first year of the vaccination programme.10 However, because of the long lead-time between infection and development of malignant disease, the programme's effect on cancer incidence will take decades to assess. Hence monitoring of cervical abnormality rates in a country such as Australia, with a longstanding high-quality cervical screening programme, is especially important because the effect on these abnormalities is more proximal than, but closely related to, the development of cervical cancer, and the treatment of such lesions is associated with morbidity and cost.
Here we present data from Victoria, reporting cervical abnormality rates in young women for the first 3 years (2007–09) after the introduction of a widely targeted population-based HPV vaccination programme.
Section snippets
Data collection
The Victorian Cervical Cytology Registry (VCCR) is one of eight Pap test registries in Australia and promotes regular participation of women in the National Cervical Screening Program by sending reminder letters and enables the follow-up of women with abnormal Pap tests. In brief, follow-up of cervical abnormalities detected by screening programmes in Australia is guided by national recommendations,11 with incident LGAs generally followed up with another smear test after 12 months to establish
Results
Table 1 shows the number of individuals included in the analysis and incidence rates for LGA and HGA diagnoses before and after introduction of the vaccination programme. Although a decrease in LGA incidence was recorded in age groups 21–25 years, 26–30 years, and 31 years and older, analysis of temporal trends suggests that these changes are a continuation of long-term trends that began before vaccination (figure 1). Figure 1 also indicates no decrease in LGA incidence in individuals aged
Discussion
This ecological analysis reports a decrease in the incidence of high-grade cervical lesions in girls aged younger than 18 years in the 3 years after the start of the HPV vaccination programme in Victoria. This decrease began soon after the introduction of the vaccination programme. In women aged 18–20 years, a decrease in incidence seems to have begun about 1·5 years after vaccine introduction. Our finding that the decrease in HGA incidence occurred in the youngest vaccination cohort before it
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