Purpose: Human Papillomavirus (HPV) infection can result in two clinical diseases of the anogenital tract, dysplasia that may result in cervical cancers and condyloma acuminata (genital warts). Clinical Trials are underway to evaluate the efficacy of an HPV vaccine for the prevention of genital warts and cervical cancers. The Merck & Co vaccine targets the HPV types that cause 70% of all cervical cancers (HPV 16 and 18) and >90% of all genital warts (HPV 6 and 11). To enable the impact of HPV vaccination to be assessed at a population level it is first necessary to have a good understanding of the natural history and burden of HPV-related diseases. The aim of this study is to develop, parameterize and validate a model of the natural history of HPV, which can be used to investigate the effectiveness of HPV vaccination at preventing infection, CIN, cervical cancer and warts in Canada.

Methods: A cohort model of the natural history of HPV infection (types 16, 18, and other Low Risk (LR) and High Risk (HR) types) and co-infection incorporating screening was developed. Model parameters were identified by fitting Canadian data on the incidence and prevalence of HPV infection, CIN, cervical cancer and warts. Model parameters (e.g. progression, regression rates) were varied between values taken from international literature. Parameter sets that minimized weighted least squares were chosen. The sensitivity of model fit to assumptions on the natural history of HPV and its parameters were assessed.

Results: A model of the natural history of HPV infection was developed. The results of the analysis will be used to identify parameters/model assumptions for which more research (data collection, modeling analysis) is needed to increase the robustness of results.

Conclusion: This natural history model can provide a solid framework to help make enlightened decisions regarding recommendation and implementation of HPV vaccination programs.