Response to "Use of cervical cancer screening among insured women: the extent of missed opportunities" [Health Policy 73 (2005) 194-201]

Epidemiologic natural history and clinical management of Human Papillomavirus (HPV) Disease: a critical and systematic review of the literature in the development of an HPV dynamic transmission model

BACKGROUND

Natural history models of human papillomavirus (HPV) infection and disease have been used in a number of policy evaluations of technologies to prevent and screen for HPV disease (e.g., cervical cancer, anogenital warts), sometimes with wide variation in values for epidemiologic and clinical inputs. The objectives of this study are to: (1) Provide an updated critical and systematic review of the evidence base to support epidemiologic and clinical modeling of key HPV disease-related parameters in the context of an HPV multi-type disease transmission model which we have applied within a U.S. population context; (2) Identify areas where additional studies are particularly needed.

METHODS

Consistent with our and other prior HPV natural history models, the literature review was confined to cervical disease and genital warts. Between October 2005 and January 2006, data were gathered from the published English language medical literature through a search of the PubMed database and references were examined from prior HPV natural history models and review papers. Study design and data quality from individual studies were compared and analyses meeting pre-defined criteria were selected.

RESULTS

Published data meeting review eligibility criteria were most plentiful for natural history parameters relating to the progression and regression of cervical intraepithelial neoplasia (CIN) without HPV typing, and data concerning the natural history of HPV disease due to specific HPV types were often lacking. Epidemiologic evidence to support age-dependency in the risk of progression and regression of HPV disease was found to be weak, and an alternative hypothesis concerning the time-dependence of transition rates is explored. No data were found on the duration of immunity following HPV infection. In the area of clinical management, data were observed to be lacking on the proportion of clinically manifest anogenital warts that are treated and the proportion of cervical cancer cases that become symptomatic by stage.

CONCLUSION

Knowledge of the natural history of HPV disease has been considerably enhanced over the past two decades, through the publication of an increasing number of relevant studies. However, considerable opportunity remains for advancing our understanding of HPV natural history and the quality of associated models, particularly with respect to examining HPV age- and type-specific outcomes, and acquired immunity following infection.

Structural differences among cost-effectiveness models of human papillomavirus vaccines

In this article we compare previously published cost-effectiveness studies of human papillomavirus (HPV) vaccines along a defined subset of key model structural assumptions relating to HPV infection and disease, cervical cancer screening and HPV vaccination. For each structural aspect examined, we summarize assumptions from each study, provide a critical review and discuss the impact upon results. Considerable variation was observed across HPV vaccine cost-effectiveness models in a number of influential assumptions. Holding constant factors for which current data are lacking, the combined impact of assumptions made for the remaining parameters examined would appear to tend toward underestimation of the cost-effectiveness of HPV vaccination within existing studies. However, uncertainty concerning parameters, such as the duration of vaccine protection and acquired immunity following HPV infection, and the relationship between age and HPV virulence, complicates precise estimation of the cost-effectiveness of HPV vaccination and rigorous evaluation of the validity of existing modeling results.