Following the introduction of a human papillomavirus (HPV) vaccination program, the incidence of high-grade cervical abnormalities—precursors to cervical cancer—fell by nearly half in girls aged 17 years and younger in the state of Victoria, Australia.

Australia introduced an HPV vaccination program, using the quadrivalent HPV vaccine, for all women aged 12 to 26 years between 2007 and 2009. Dr. Julia M.L. Brotherton, BMed, of the Victorian Cytology Service Registries in East Melbourne, Victoria, Australia, and colleagues analyzed trends in both low-grade and high-grade cervical abnormalities in the women of Victoria before (January 1, 2003, through March 31, 2007) and after (April 1, 2007, through December 31, 2009) the introduction of the vaccination program.

Using data from the Victorian Cervical Cytology Registry for women in five age groups, Brotherton and co-investigators noted the decline in incidence of high-grade cervical abnormalities (HGAs; cervical intraepithelial neoplasia of grade 2 or worse or adenocarcinoma in situ) in screened females younger than age 18 years from 80% before program implementation to 42% after. No decline was seen in older age groups or for low-grade cervical abnormalities (LGAs).

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“Our finding that the decrease in HGA incidence occurred in the youngest vaccination cohort before it occurred in the older, catch-up cohorts (who were more likely to have been previously sexually experienced) reinforces the appropriateness of the targeting of prophylactic HPV vaccines to preadolescent girls,” wrote the authors in The Lancet (2011;377[9783]:2085-2092). However, they caution that “Linkage between vaccination and screening registers is needed to confirm that this ecological observation is because of vaccination and to monitor participation in screening.”