Cervical Intraepithelial Neoplasia Rates in British Columbia Women: A Population-Level Data Linkage Evaluation of the School-Based HPV Immunization Program

Abstract Background To understand real-world human papillomavirus (HPV) vaccine impact, continuous evaluation using population-based data is critical. We evaluated the early impact of the school-based HPV immunization program on cervical dysplasia in women in British Columbia, Canada. Methods Data linkage was performed using records from provincial cervical screening and immunization registries. Precancerous outcomes were compared between unvaccinated and HPV-vaccinated women born 1994–2005. Incidence rate, relative rate (RR), and vaccine effectiveness (VE), using unadjusted and adjusted Poisson regression of cytology (HSIL) and histopathology (CIN2, CIN3, and CIN2+) outcomes, were compared across vaccination status groups. Results Women who received a complete series of vaccine on schedule between age 9 and 14 years had an adjusted RR = 0.42 (95% confidence interval [CI], 0.31–0.57) for CIN2+ over 7 years of follow-up compared to unvaccinated women, resulting in a VE of 57.9% (95% CI, 43.2%–69.0%). Adjusted RR for HSIL was 0.53 (95% CI, .43–.64), resulting in a VE of 47.1% (95% CI, 35.6%–56.7%). Conclusion Women vaccinated against HPV have a lower incidence of cervical dysplasia compared to unvaccinated women. Immunization between 9 and 14 years of age should be encouraged. Continued program evaluation is important for measuring long-term population impact.