The early benefits of human papillomavirus vaccination on cervical dysplasia and anogenital warts.

BACKGROUND Despite widespread promotion of quadrivalent human papillomavirus (qHPV) vaccination for young girls, there is limited information on the vaccine's real-world effectiveness and none on the effectiveness of qHPV vaccination programs. We assessed the impact of the qHPV vaccine and Ontario's grade 8 qHPV vaccination program on cervical dysplasia and anogenital warts (AGW). METHODS By using administrative health databases of Ontario, Canada, we identified a population-based retrospective cohort of girls in grade 8 before (2005/2006-2006/2007) and after (2007/2008-2008/2009) program implementation. Vaccine exposure was ascertained in grades 8 to 9 and outcomes in grades 10 to 12. A quasi-experimental approach known as regression discontinuity was used to estimate absolute risk differences (RDs), relative risks (RRs), and 95% confidence intervals (CIs) attributable to vaccination and program eligibility (intention-to-treat analysis). RESULTS The cohort comprised 131,781 ineligible and 128,712 eligible girls (n = 260,493). We identified 2436 cases of dysplasia and 400 cases of AGW. Vaccination significantly reduced the incidence of dysplasia by 5.70 per 1000 girls (95% CI -9.91 to -1.50), corresponding to a relative reduction of 44% (RR 0.56; 95% CI 0.36 to 0.87). Program eligibility also had a significant protective effect on dysplasia: RD -2.32/1000 (95% CI -4.02 to -0.61); RR 0.79 (95% CI 0.66 to 0.94). Results suggested decreases in AGW attributable to vaccination (RD -0.83/1000, 95% CI -2.54 to 0.88; RR 0.57, 95% CI 0.20 to 1.58) and program eligibility (RD -0.34/1000, 95% CI -1.03 to 0.36; RR 0.81, 95% CI 0.52 to 1.25). CONCLUSIONS This study provides strong evidence of the early benefits of qHPV vaccination among girls aged 14 to 17 years, offering additional justification for not delaying vaccination.