www.thelancet.com/infection Published online July 20, 2015 http://dx.doi.org/10.1016/S1473-3099(15)00055-9 1 Articles Lancet Infect Dis 2015 Published Online July 20, 2015 http://dx.doi.org/10.1016/ S1473-3099(15)00055-9 See Online/Comment http://dx.doi.org/10.1016/ S1473-3099(15)00085-7 Melbourne Sexual Health Centre, Alfred Health, Carlton, Melbourne, VIC, Australia (E P F Chow PhD, G Fehler MSc, C S Bradshaw PhD, M Y Chen PhD, Prof C K Fairley PhD); Central Clinical School, Faculty of Medicine, Nursing and Health Sciences, Monash University, Melbourne, VIC, Australia (E P F Chow, C S Bradshaw, M Y Chen, Prof C K Fairley); Department of Microbiology and Infectious Diseases, Royal Women’s Hospital, Parkville, Melbourne, VIC, Australia (J A Danielewski PhD, S N Tabrizi PhD, Prof S M Garland MD); Murdoch Childrens Research Institute, Parkville, Melbourne, VIC, Australia (J A Danielewski, S N Tabrizi, Prof S M Garland); Department of Obstetrics and Gynaecology, University of Melbourne, Parkville, Melbourne, VIC, Australia (S N Tabrizi, Prof S M Garland); and Kirby Institute, University of New South Wales Australia, Sydney, NSW, Australia (Prof M G Law PhD) Correspondence to: Dr Eric P F Chow, Melbourne Sexual Health Centre, Alfred Health, Carlton, Melbourne, VIC 3053, Australia echow@mshc.org.au Human papillomavirus in young women with Chlamydia trachomatis infection 7 years after the Australian human papillomavirus vaccination programme: a cross-sectional study Eric P F Chow, Jennifer A Danielewski, Glenda Fehler, Sepehr N Tabrizi, Matthew G Law, Catriona S Bradshaw, Suzanne M Garland, Marcus Y Chen, Christopher K Fairley Summary Background The national quadrivalent human papillomavirus (4vHPV) vaccination programme was launched in Australia in April, 2007. In this study, we aimed to explore the prevalence of vaccine-targeted human papillomavirus (HPV) types contained in the 4vHPV and nine-valent HPV (9vHPV) vaccines detected in young women diagnosed with chlamydia. Methods In this cross-sectional study, we identified specimens from women aged 25 years or younger who attended the Melbourne Sexual Health Centre (Melbourne, VIC, Australia) diagnosed with chlamydia. We calculated the prevalence of 4vHPV types (6, 11, 16, and 18) and the extra five 9vHPV types (31, 33, 45, 52, and 58 alone) excluding 4vHPV types, stratified by Australian financial year (and according to the prevaccination and postvaccination periods) and self-reported vaccination status, for all women, Australian-born women, Australian-born women aged 21 years and younger, and overseas-born women. We calculated adjusted prevalence ratios using binomial log linear regression. Findings Between July 1, 2004, and June 30, 2014, we included 1202 women. The prevalence of 4vHPV types in Australian-born women decreased during this period (HPV 6 and 11: 2004–05 nine [16%, 95% CI 8–28] of 56 vs 2013–14 one [2%, 0–9] of 57, p<0·0001; HPV 16 and 18: 17 [30%, 19–44] vs two [4%, 0–12], p<0·0001). In Australian-born women aged 21 years and younger, HPV 6 and 11 prevalence remained at 0% for all years after 2008–09, and we detected HPV 16 and 18 in 5% or less of samples for the same period. In unvaccinated Australian-born women, we noted a significant decrease in 4vHPV types from 66 (41%, 95% CI 34–49) of 160 in the prevaccination period (from July 1, 2004, to June 30, 2007) to five (19%, 6–38) of 27 in the postvaccination period (July 1, 2007, to June 30, 2014; p=0·031), but not in the 9vHPV types, excluding 4vHPV (36 [23%, 95% CI 16–30] vs seven [26%, 11–46]; p=0·805). Interpretation The three-dose vaccination coverage was sufficient for the 4vHPV types to almost disappear in Australian-born women aged 21 years or younger within 3 years of introduction of the national HPV vaccination programme. We noted strong herd protection, with a significant decrease in the prevalence of 4vHPV in unvaccinated women. The 4vHPV vaccination programme in Australia has been successful at protecting women against 4vHPV types. Funding Australian National Health and Medical Research Council. Introduction Human papillomavirus (HPV) is one of the most common sexually transmitted infections worldwide, and women aged 25 years and younger are at high risk. 1,2 Worldwide HPV prevalence in women is esti- mated at about 10%, but substantial geographical variation exists, from 32% in eastern Africa to 6% in southeastern Asia. 1 HPV 16 and 18 are generally the two most common types. 1,3 Currently, three HPV vaccines are available worldwide. The bivalent HPV vaccine (Cervarix; GlaxoSmithKline, Boronia, VIC, Australia) can protect against HPV 16 and 18, whereas the quadrivalent HPV (4vHPV) vaccine (Gardasil; CSL, Parkville, VIC, and Merck, Macquarie Park, NSW, Australia) can protect against HPV 6, 11, 16, and 18. A nine-valent HPV (9vHPV) vaccine, which includes types 6, 11, 16, 18, 31, 33, 45, 52, and 58, protecting against the five additional high-risk cancer-causing HPV types, was approved by the US Food and Drug Administration in 2014 (Gardasil 9), 4 but is not currently used in Australia. A meta-analysis of 20 studies from nine high-income countries 5 showed that HPV 16 and 18 decreased in women by 68% and anogenital warts by 61% after introduction of HPV vaccines. In April, 2007, Australia became the first country to introduce a free national HPV vaccination programme. Girls aged 12–13 years were eligible for the 4vHPV vaccine at school. The programme was free of charge, with a catch-up programme for women and girls aged 13–26 years through general practice and community immunisation clinics from July, 2007, to 2009. 6 The