Early effect of the HPV vaccination programme on cervical abnormalities in Victoria, Australia: an ecological study

Background Australia introduced a human papillomavirus (HPV) vaccination programme with the quadrivalent HPV vaccine for all women aged 12-26 years between 2007 and 2009. We analysed trends in cervical abnormalities in women in Victoria, Australia, before and after introduction of the vaccination programme. Methods With data from the Victorian Cervical Cytology Registry between 2003 and 2009, we compared the incidence of histopathologically defined high-grade cervical abnormalities (HGAs, lesions coded as cervical intraepithelial neoplasia of grade 2 or worse or adenocarcinoma in situ; primary outcome) and low-grade cytological abnormalities (LGAs) in five age groups before (Jan 1, 2003, to March 31, 2007) and after (April 1, 2007, to Dec 31, 2009) the vaccination programme began. Binary comparisons between the two periods were done with Fisher's exact test. Poisson piecewise regression analysis was used to compare incident rate trends. Findings After the introduction of the vaccination programme, we recorded a decrease in the incidence of HGAs by 0.38% (95% CI 0.61-0.16) in girls younger than 18 years. This decrease was progressive and significantly different to the linear trend in incidence before introduction of the vaccination (incident rate ratio 1.14, 1.00-1.30, p=0.05). No similar temporal decline was recorded for LGAs or in older age groups. Interpretation This is the first report of a decrease in incidence of HGAs within 3 years after the implementation of a population-wide HPV vaccination programme. Linkage between vaccination and screening registers is needed to confirm that this ecological observation is attributable to vaccination and to monitor participation in screening among vaccinated women.